public static void displayDetails(Rental r) {
   System.out.println("\nContract #" + r.getContractNumber());
   System.out.println(
       "For a rental of "
           + r.getHours()
           + " hours and "
           + r.getExtraMinutes()
           + " minutes, at a rate of "
           + r.HOUR_RATE
           + " the price is $"
           + r.getPrice());
 }