    private String calculate() {
    	double money, buy_p, sell_p, ticket, tax;
    	try {
	    	money  = Double.parseDouble(i_money.getText().toString());
	    	buy_p  = Double.parseDouble(i_buy_p.getText().toString());
	    	sell_p = Double.parseDouble(i_sell_p.getText().toString());
	    	if(i_tax.getCheckedRadioButtonId() == i_tax_none.getId()) {
	    		tax = 0;
	    	} else if(i_tax.getCheckedRadioButtonId() == i_tax_cust.getId()) {
	    		tax = Double.parseDouble(i_cust_tax.getText().toString());
	    	} else {
	    		tax = 0;
	    	}
	    	ticket = Double.parseDouble(i_ticket.getText().toString());
    	} catch (NumberFormatException e) {
    		return "Please fill with valid information";
    	}
    	int amount = (int) Math.floor(money / buy_p);
    	double expenditure = amount * buy_p - 2 * ticket;
    	double revenue_taxless = amount * sell_p;
    	double revenue = amount * sell_p * (1 / (1 + tax / 100));
    	double income = revenue - expenditure;
    	return "You get: " 			+ amount 	+ " items\n" +
    		   "They cost (inc. travel): " + expenditure + "\n" +
    		   "They sell for: " 	+ revenue_taxless    + "\n" +
    		   "Profit: " 			+ income;
    }

    private String calculate() {
    	double money, buy_p, sell_p, ticket, tax;
    	try {
	    	money  = Double.parseDouble(i_money.getText().toString());
	    	buy_p  = Double.parseDouble(i_buy_p.getText().toString());
	    	sell_p = Double.parseDouble(i_sell_p.getText().toString());
	    	if(i_tax.getCheckedRadioButtonId() == i_tax_none.getId()) {
	    		tax = 0;
	    	} else if(i_tax.getCheckedRadioButtonId() == i_tax_cust.getId()) {
	    		tax = Double.parseDouble(i_cust_tax.getText().toString());
	    	} else {
	    		tax = 0;
	    	}
	    	ticket = Double.parseDouble(i_ticket.getText().toString());
    	} catch (NumberFormatException e) {
    		return "Please fill with valid information";
    	}
    	int amount = (int) Math.floor(money / buy_p);
    	double expenditure = amount * buy_p + 2 * ticket;
    	double revenue_taxless = amount * sell_p;
    	double revenue = amount * sell_p * (1 / (1 + tax / 100));
    	double income = revenue - expenditure;
    	return "You get: " 			+ amount 	+ " items\n" +
    		   "They cost (inc. travel): " + expenditure + "\n" +
    		   "They sell for: " 	+ revenue_taxless    + "\n" +
    		   "Profit: " 			+ income;
    }
