If the total revenue received from the sale of x items is given by R(x) = 40 In (3x + 1), while the total cost to produce X x items is C(x) = 7, find the following. (a) The marginal revenue (b) The profit function P(x) (c) The marginal profit when x = 120 (d) Interpret the results of part (c). . . . (a) How can the marginal revenue be found? O A. Find R(x) - C(x). O B. Find R O c. Find the derivative of R(x). O D. Find the derivative of R(x) - C(x)