Android : Eclipse Android Boot Camp- How to modify the Ferry app?

Afternoon all, I am new to Java Programming and am currently studying in this field. The mentor has asked that we create a simple app that allows user to enter amount of tickets and click to compute cost at a set rate of $18 for the two locations. We have been asked to outsource and research to complete the app; so that tickets to (1)Cape Marie cost $20 and tickets to (2)Star Island cost $30. Any help would be greatly appreciated my code is below;

public class MainActivity extends Activity 
{
    double costPerTicket=18.00;
    int numberOfTickets;
    double totalCost;
    String groupChoice;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final EditText tickets=(EditText)findViewById(R.id.txtTickets);
        final Spinner group=(Spinner)findViewById(R.id.txtGroup);
        Button cost = (Button)findViewById(R.id.btnCost);
        cost.setOnClickListener(new OnClickListener()
        {
            final TextView result=((TextView)findViewById(R.id.txtResult));
            @Override
            public void onClick(View v)
            {
                // TODO Auto-generated method stub
                numberOfTickets=Integer.parseInt(tickets.getText().toString());
                totalCost=costPerTicket * numberOfTickets;
                DecimalFormat currency=new DecimalFormat("$###,###.##");
                groupChoice=group.getSelectedItem().toString();
                result.setText("Total cost for "+groupChoice +" is " +currency.format(totalCost));
            }
        });
    }