private EditText money, procent;
    private TextView answer;
    private Button btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_calculator);
        init();
        btn.setOnClickListener(v -> answer());
    }

    private void init() {
        money = findViewById(R.id.money);
        procent = findViewById(R.id.procent);
        answer = findViewById(R.id.answer);
        btn = findViewById(R.id.btn);
    }

    private void answer(){
        System.out.println("===================== "+money.getText().toString());
        int qwe = Integer.parseInt(money.getText().toString());
        System.out.println(qwe);
        int asd = Integer.parseInt(procent.getText().toString());
        int Answer = qwe * asd / 100;
        answer.setText(String.valueOf(Answer));
    }





<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_row="2"
    tools:context=".calculator">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/first">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Procent:" />

        <EditText
            android:id="@+id/procent"
            android:layout_width="200px"
            android:layout_height="wrap_content" />

    </LinearLayout>



    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/first"
        android:id="@+id/second">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="50px"
            android:text="Money:" />

        <EditText
            android:id="@+id/money"
            android:layout_width="200px"
            android:layout_height="wrap_content" />

    </LinearLayout>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/second"
        android:id="@+id/btn"
        android:text="Go"
        />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/second"
        android:layout_marginTop="150px">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="50px"
            android:text="Answer:" />

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/answer"/>

    </LinearLayout>



</RelativeLayout>