Suppose that x and y represent the amounts of two basic inputs for a production process and that the equation 56x y 5/8 3/8 = 12,485 describes all input amounts where the output of the process is 12,485 units. a) Find dy dx b) What is the marginal rate of substitution of x for y when x = 625 and y = 40? . . . =(Simplify your answer.) 4 a dx b) The marginal rate of substitution of x for y when x = 625 and y = 40 is (Simplify your answer.)