// Write a method called calculateTotalPayment that takes two
    // arguments, an int meal which is the cost of a meal, and a
    // double tip which represents the tip percentage one would add to
    // the bill.
    // The method must return a double which equals how much should be
    // paid.
    //
    // int meal must be greater than 0
    // double tip must be 0 or greater and .7 or less (no tips over 70%)
    // If either number is invalid, return -1;
    //
    // Don't forget to use the public static modifiers



 public static double calculateTotalPayment(int x, double tip){
        double total;
        total = 0;
        if((x > 0) && (tip < 0.7) && (tip >= 0)) {
            total = x + (tip * total);
        }
        else {
            total = -1;
        }
        return total;
    }