The function C gives the production cost for a bakery to produce cakes of a certain type, where C (x) is the cost, in dollars, to produce x of the cakes. The function M defined by M (x) = C (x + 1) – C (x) gives the marginal cost, in dollars, to produce cake number x + 1. Which of the following gives the best estimate for the marginal cost, in dollars, to produce the 40th - cake?
