John consumes only two goods, pizza (P) and hamburgers (H) and considers them to

be perfect substitutes, as shown by his utility function: U(P, H) = P + 8H. The price of pizza

is N$4 and the price of hamburgers is N$8, and Paul's monthly income is N$400. Knowing that

he likes pizza, John's grandmother gives him a birthday gift certificate of N$80 redeemable

only at Pizza Hut. Though John is happy to get this gift, his grandmother did not realize

that she could have made him exactly as happy by spending far less than she did. How

much would she have needed to give him in cash to make him just as well off as with the

gift certificate?