Bart's expenditure function for two goods, x and y, as a function of their prices and a specified level of utility , is e(px, py, ) = /PxPy. Lisa's utility function is U(x, y) = 7xy" for some value of a. a) What are Bart's Marshallian demand functions for each of x and y? Assume that he gets an allowance from his parents (i.e., exogenous income) of Mg. You can denote these functions as x and yg. (5 points) b) What are Lisa's Marshallian demand functions for each of x and y? Assume that she gets an allowance from her parents (i.e., exogenous income) of M. You can denote these functions as xi and yi. (5 points) c) Bart and Lisa's mother, Marge, has noticed that their combined consumptions, x + x and YB + YL, only depend on the sum total of their allowances, M = Mg + M; in other words, it does not depend on how M is distributed between Bart and Lisa. What must the value of a be for this to be true? Show your work. (5 points)