John consumes two goods,X and Y.The marginal utility of X and the marginal utility of Y satisfy the following equations: MUX = Y MUY = X. The price of X is $9,and the price of Y is $12. a.Write an expression for John's MRS. b.What is the optimal mix between X and Y in John's market basket? c.John is currently consuming 15 X and 10 Y per time period. Is he consuming an optimal mix of X and Y?