نحوه انجام عملیات ریاضی و نمایش دادن

 public class ActivityGetTime extends Activity {
     int a1;
     int a2;
     int a3;
    int b;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final EditText edt1 = (EditText) findViewById(R.id.edt1);
        final EditText edt2 = (EditText) findViewById(R.id.edt2);
        final EditText edt3 = (EditText) findViewById(R.id.edt3);
        final TextView txt = (TextView) findViewById(R.id.txt);
        Button btn = (Button) findViewById(R.id.btn);
        
         
        //a1 = pasokhe dorost
        //a2 = pasokhe eshtebah
        //a3 = tedade kol soalat
        //b = result
        btn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                a1 = Integer.parseInt(edt1.getText().toString());
                a2 = Integer.parseInt(edt2.getText().toString());
                a3 = Integer.parseInt(edt3.getText().toString());

                b = (((a1 * 3) - a2) * 100) / (a3 * 3);
                txt.setText("" + b);

            }
        });
        

    }
}