Andy purchases only two goods, apples (a) and kumquats (k). he has an income of $125 and can buy apples at $5 per pound and kumquats at $5 per pound. his utility function is u(a, k) = 6a + 2k. what is his marginal utility for apples and his marginal utility for kumquats? andy's marginal utility for apples (mu subscript a) is mu subscript aequals 6 and his marginal utility for kumquats (mu subscript k) is