Number of milkshakes Marginal utility of milkshakes Number of coffees Marginal utility of burgers 0 0 1 36 1 45 2 32 2 40 3 28 3 35 4 24 4 30 5 20 5 25 6 16 6 20 7 12 7 15 8 8 8 10 Duncan's marginal utilities for milkshakes and burgers are given in the table. The price of a milkshake is R4, and the price of a burger is R5. If Duncan's income is R25, to maximise his utility, he buys Answer shake(s) and Answer burger(s)