George finds he can wash 10 cars and wax 5 cars in one 8-hour shift. In the same 8-hour shift he could wash 8 cars and wax 6 cars.

George finds he can wash 10 cars and wax 5 cars in one 8-hour shift.  In the same 8-hour shift he could wash 8 cars and wax 6 cars.  If George has constant opportunity cost and wants to wash 4 cars he can expect to be able to wax ____ cars.  Enter a whole number for your answer such as 12.