The total cost (in dollars) of producing x food processors is C(x) = 2400 + 20x -0.4x. (A) Find the exact cost of producing the 21st food processor. (B) Use the marginal cost to approximate the cost of producing the 21st food processor. (A) The exact cost of producing the 21st food processor is $ (B) Using the marginal cost, the approximate cost of producing the 21st food processor is $