Android Studio Simple TaxiMeter : Good evening,

l am trying to learn Android Studio. l have limited information about Java, l searched everywhere to solve this but l keep receivin error and couldn't fix it on my own. l want to make a simple calculator. Customer will enter the how many kilometers he/she went and the calculator will give the total amount. The opening amount is 4 and the rate per km is 1.4. 

What am l doing wrong? Please let me know. 

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        double km;
        int y;
        double x;
        x = 1.4;
        y = 4;

        TextView tabela = (TextView) findViewById(R.id.tabela);
        EditText number = (EditText) findViewById(R.id.number);
        String written = number.getText().toString();
        km = Double.parseDouble(written);
        tabela.setText("Total Amount" + ((km*x)+y));
    }
}