In the design of an automobile radiator, an engineer has a choice of using either a brass-copper alloy casting or plastic modeling. Either the material provides the same service. However, the brass-copper alloy weighs 25 pounds, compare with the 20 pounds of plastic molding. Every pound of an extra pound in automobile has been assigned penalty of $6 to the account due to fuel consumption during the life cycle of the car. The brass copper alloy casting cost $3.35 per pound whereas plastic molding cost $7.40 per pound. Machining cost per casting are $6 for the brass copper alloy. Which material should the engineer select. What is the difference in unit cost.