Code for simple Android control car

//Author riham
char l;
void setup() {
  Serial.begin(9600);
  // put your setup code here, to run once:
  pinMode(3,OUTPUT); // For Ena
  pinMode(4,OUTPUT); //In1
  pinMode(5,OUTPUT); // In2
  pinMode(6,OUTPUT); //In3
  pinMode(7,OUTPUT); // In4
  pinMode(9,OUTPUT); // For Enb

}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(3,HIGH); // controls the speed of motor A
  digitalWrite(9,HIGH);//controls the speed of motor B

   if(Serial.available()){
    l = Serial.read(); // Reads from bluetooth
      //forward
    if(l == 'F'){
  digitalWrite(5,HIGH);
  digitalWrite(4,LOW);
  digitalWrite(6,HIGH);
  digitalWrite(7,LOW);
  }
  //backward
 else if(l == 'B'){
  digitalWrite(5,LOW);
  digitalWrite(4,HIGH);
  digitalWrite(6,LOW);
  digitalWrite(7,HIGH);

    }
    //Left
   else if(l == 'L'){
  digitalWrite(5,HIGH);
  digitalWrite(4,LOW);
  digitalWrite(6,LOW);
  digitalWrite(7,LOW);
  }
  //Right
   else if(l == 'R'){
  digitalWrite(5,LOW);
  digitalWrite(4,LOW);
  digitalWrite(6,HIGH);
  digitalWrite(7,LOW);
  }
  //Stop
      else{
  digitalWrite(5,LOW);
  digitalWrite(4,LOW);
  digitalWrite(6,LOW);
  digitalWrite(7,LOW);
    }
   }

}