11.13. A monopolist serves a market in which the demand is P ! 120 " 2Q. It has a fixed cost of 300. Its marginal cost is 10 for the first 15 units (MC ! 10 when 0 $ Q $ 15). If it wants to produce more than 15 units, it must pay overtime wages to its workers, and its marginal cost is then 20. What is the maximum amount of profit the firm can earn?