pls work thnx

import java.util.*;

public class FinalProject {


    public static String [][] matrix = new String [21][10];
    public static Scanner sc = new Scanner(System.in);


    public static void main(String[] args) {
        matrix[0][0]="Students";
        matrix[0][1]="Homework 1";
        matrix[0][2]="Homework 2";
        matrix[0][3]="Homework 3";
        matrix[0][4]="Homework 4";
        matrix[0][5]="First Exam";
        matrix[0][6]="Second Exam";
        matrix[0][7]="Final Project";
        matrix[0][8]="Final Exam";
        matrix[0][9]="Final Grade";

        for(int i=1;i<21;i++){
            matrix[i][0]="empty";
            for(int j=1;j<10;j++)
                matrix[i][j]="0";
        }

        int option = 0;
        while (option != 7){
            System.out.println ("***************************************\n"+
                    "1.- Enter student information.\n"+
                    "2.- Enter student grades. \n"+
                    "3.- Student grade report.\n"+
                    "4.- Activity grade report.\n"+
                    "5.- Group performance.\n"+
                    "6.- Print matrix.\n"+
                    "7.- Exit Menu\n"+
                    "***************************************\n");


            option = sc.nextInt();

            switch(option){
                case 1:
                    studentInformation();
                    break;
                case 2:
                    studentGrades();
                    break;
                case 3:
                    studentReport();
                    break;
                case 4:
                    activityReport();
                    break;
                case 5:
                    groupPerformance();
                    break;
                case 6:
                    printMatrix();
                    break;
            }
        }

    }


     public static void studentInformation(){
         System.out.print("Select the number of the student you want (1-20) you can type 0 if you don't know the number you are at: ");
        int student = sc.nextInt();

        System.out.print("Enter student name: ");
        String name = sc.next();

        if(student != 0){
            matrix[student][0] = name;
        }
        else{
            int indice = -1;
            for (int i = 0; i <  matrix.length; i++) {
                if( "empty".equals(matrix[i][0])){
                    indice = i;
                    break;
                }
            }
            if(indice != -1){
                 matrix[indice][0] = name;
            }
            else{
                System.out.println("The matrix is full.");
            }
        }
     }

    public static void studentGrades(){
        System.out.print("Select the number of the student you want: ");
        int student = sc.nextInt();

       System.out.println ("***************************************\n"+
                    "Select the action you want: \n"+
                    "1.- Enter 1st homework grade. \n"+
                    "2.- Enter 2nd homework grade. \n"+
                    "3.- Enter 3rd homework grade. \n"+
                    "4.- Enter 4th homework grade. \n"+
                    "5.- Enter 1st exam grade. \n"+
                    "6.- Enter 2nd exam grade. \n"+
                    "7.- Enter final project grade. \n"+
                    "8.- Enter final exam grade. \n"+
                    "***************************************\n");
        int option = sc.nextInt();

            switch(option){
                case 1:
                    System.out.print("Enter grade: ");
                    String hw1 = sc.next();
                    matrix[student][1] = hw1;
                    break;
                case 2:
                    System.out.print("Enter grade: ");
                    String hw2 = sc.next();
                    matrix[student][2] = hw2;
                    break;
                case 3:
                    System.out.print("Enter grade: ");
                    String hw3 = sc.next();
                    matrix[student][3] = hw3;
                    break;
                case 4:
                    System.out.print("Enter grade: ");
                    String hw4 = sc.next();
                    matrix[student][4] = hw4;
                    break;
                case 5:
                    System.out.print("Enter grade: ");
                    String ex1 = sc.next();
                    matrix[student][5] = ex1;
                    break;
                case 6:
                    System.out.print("Enter grade: ");
                    String ex2 = sc.next();
                    matrix[student][6] = ex2;
                    break;
                case 7:
                    System.out.print("Enter grade: ");
                    String fp = sc.next();
                    matrix[student][7] = fp;
                    break;
                case 8:
                    System.out.print("Enter grade: ");
                    String fe = sc.next();
                    matrix[student][8] = fe;
                    break;
            }
    }

    public static void studentReport(){
        System.out.print("Select the number of the student you want: ");
        int student = sc.nextInt();

        System.out.println ("***************************************\n"+
                    "Select the action you want to perform:\n"+
                    "1.- Final score. \n"+
                    "2.- Activity scores. \n"+
                    "***************************************\n");
        int option = sc.nextInt();

        if(option == 2){
            System.out.println ("***************************************\n"+
                    "Select the activity you want to print: \n"+
                    "1.- 1st homework grade. \n"+
                    "2.- 2nd homework grade. \n"+
                    "3.- 3rd homework grade. \n"+
                    "4.- 4th homework grade. \n"+
                    "5.- 1st exam grade. \n"+
                    "6.- 2nd exam grade. \n"+
                    "7.- Final project grade. \n"+
                    "8.- Final exam grade. \n"+
                    "***************************************\n");
        int option2 = sc.nextInt();
            switch(option2){
                case 1:
                    System.out.print("The 1st homework grade for " + matrix[student][0] + " is: " + matrix[student][1]);
                    break;
                case 2:
                    System.out.print("The 2nd homework grade for " + matrix[student][0] + " is: " + matrix[student][2]);
                    break;
                case 3:
                    System.out.print("The 3rd homework grade for " + matrix[student][0] + " is: " + matrix[student][3]);
                    break;
                case 4:
                    System.out.print("The 4th homework grade for " + matrix[student][0] + " is: " + matrix[student][4]);
                    break;
                case 5:
                    System.out.print("The 1st exam grade for " + matrix[student][0] + " is: " + matrix[student][5]);
                    break;
                case 6:
                    System.out.print("The 2nd exam grade for " + matrix[student][0] + " is: " + matrix[student][6]);
                    break;
                case 7:
                    System.out.print("The final project grade for " + matrix[student][0] + " is: " + matrix[student][7]);
                    break;
                case 8:
                    System.out.print("The final exam grade for " + matrix[student][0] + " is: " + matrix[student][8]);
                    break;
            }
        }

        else {
            String grade = finalGrade(student);

            System.out.println("The final grade of " + matrix[student][0] + " is: " + grade);
                }
    }

    public static void activityReport(){

       System.out.println ("***************************************\n"+
                    "Select the number of the activity you want:\n"+
                    "1.- 1st homework grade. \n"+
                    "2.- 2nd homework grade. \n"+
                    "3.- 3rd homework grade. \n"+
                    "4.- 4th homework grade. \n"+
                    "5.- 1st exam grade. \n"+
                    "6.- 2nd exam grade. \n"+
                    "7.- Final project grade. \n"+
                    "8.- Final exam grade. \n"+
                    "***************************************\n");
        int activity = sc.nextInt();

        System.out.println ("***************************************\n"+
                    "Select the action youw ant to perform:\n"+
                    "1.- Activity Average. \n"+
                    "2.- Activity Variance. \n"+
                    "3.- Activity Standard Deviation. \n"+
                    "***************************************\n");
        int option = sc.nextInt();

        int[] grade = new int[20];
        int sum=0;
        int numberGrades=0;
        int average=-1;
        int sumvariance = 0;
        int variance = 0;

        for(int i=1;i<21;i++){
            grade[i-1]=Integer.parseInt(matrix[i][activity]);
        }

        for(int i=0;i<20;i++){
             if(grade[i]!=-1){
                 sum += grade[i];
                 numberGrades++;
             }
        }
        if(numberGrades!=0){
            average = sum/numberGrades;
        }

        for(int i=0;i<20;i++){
            if(grade[i]!=-1){
                sumvariance+=(int) Math.pow((grade[i] - average),2);
            }
        }

        if(numberGrades!=0){
            variance=sumvariance/numberGrades;
        }
        int dev=(int)Math.sqrt(variance);
        switch(option){
            case 1:
                System.out.println("The activity average is: " + average);
                break;
            case 2:
                System.out.println("The activity variance is: " + variance);
                break;
            case 3:
                System.out.println("The activity Standard Deviation is: " + dev);
                break;
        }
    }


    public static void groupPerformance(){
        int[] grade= new int [20];
        for(int i=1; i<21;i++)
            grade[i-1]=Integer.parseInt(finalGrade(i));

        System.out.println ("***************************************\n"+
                    "What would you like to know?\n"+
                    "1.- Group average \n"+
                    "2.- Group Variance \n"+
                    "3.- Group Standard Deviation \n"+
                    "4.- Number of students that passed and number of stufents that failed. \n"+
                    "***************************************\n");
        int option =sc.nextInt();
        int sum=0;
        int numberGrades=0;
        int groupaverage=-1;
        int sumvariance = 0;
        int variance = 0;

        for(int i=0;i<20;i++){
             if(grade[i]!= 0 ){
                 sum += grade[i];
                 numberGrades++;
             }
        }
        if(numberGrades!=0){
            groupaverage = sum/numberGrades;
        }

        for(int i=0;i<20;i++){
            if(grade[i]!= 0){
                sumvariance += (int) Math.pow((grade[i]-groupaverage),2);
            }
        }

        if(numberGrades!=0){
            variance = sumvariance/numberGrades;
        }
        int dev=(int)Math.sqrt(variance);

        switch(option){
            case 1:
                System.out.println("The group Average is: " + groupaverage);
                break;
            case 2:
                System.out.println("The group Variance is: "+ variance);
                break;
            case 3:
                System.out.println("The group Standard Deviation is: "+ dev);
                break;

            case 4:
                int p=0;
                int f=0;
                for(int i=0;i<20;i++){
                    if(grade[i]!= 0 & grade[i]<70){
                        f++;
                    }
                    if(grade[i]!= 0 & grade[i]>=70){
                        p++;
                    }
                }
                System.out.println("Number of students that passed: " + p + "\nNumber of students that failed: " + f);
                break;
        }
    }



    public static void printMatrix(){
        for (final Object[] row : matrix) {
            System.out.format("%15s%15s%15s%15s%15s%15s%15s%18s%15s%15s\n", row);
            }
    }

    public static String finalGrade (int student){
            int[] grade = new int[10];
            int suma = 0;
            double c = 0;
            double c2 = 0;
            double c3 = 0;
            double c4 = 0;
            for(int i=1;i<10;i++){
                grade[i-1]=Integer.parseInt(matrix[student][i]);
            }
            for(int i=1;i<9;i++){
                if(i<=4){
                    suma += grade[i];
                    c = suma/4;
                    c = c*0.4;
                }
                else if (i>4&&i<=6){
                    suma = 0;
                    suma += grade [i];
                    c2 = suma/2;
                    c2 = c2*0.15;
                }
                else if (i==7){
                    c3 = grade [i]*0.25;
                }
                else if (i==8){
                    c4 = grade [i]*0.20;
                }
            }
                double finalg = c + c2 + c3 + c4;
                return matrix[student][9]=Double.toString(finalg);
            }

}