JButton btn = new JButton("OK");
btn.addActionListener(
     new ActionListener(){
         public void actionPerformed(ActionEvent e){

         String currentCountry = (String)cb.getSelectedItem();
         double percentage = 0.00;

           if(currentCountry.equals("Brazil") || currentCountry.equals("Argentina")) {
            cb2.removeAllItems();
            for(int i = 0; i < choicesSouthAmerica.length; i++) {
                cb2.addItem(choicesSouthAmerica[i]);
            }
        }
        else {
            cb2.removeAllItems();
            for(int i = 0; i < choicesEurope.length; i++) {
                cb2.addItem(choicesEurope[i]);
            }
        }

    btn.setEnabled(false);
    btn2.setEnabled(true);
        if(currentCountry.equals("Brazil") || currentCountry.equals("Argentina")){
            percentage = 1/5;

        }
        else{
            percentage = 1/8;

        }
    }


            }



    );