Monopolistic Competition Please submit your answer to the extra credit question separately. Consider the following application of monopolistic competition in trade. Firms in an industry face monopolistic competition and the (residual) demand function of a firm's product is: 1 Q=S nb(PP) where Q is the quantity of output demanded, S is the total output of the industry, n is the number of firms in the industry, b is a positive constant term representing the responsiveness of a firm's sales to its price, P is the price charged by the firm itself, and P is the average price charged by firms in this industry. Firms are small, so each firm treats P as given ( a firm does not think its own pricing strategy changes P ). Each firm faces the same residual demand curve. They also have the same fixed cost F. Marginal cost is a constant. However, firms cannot observe their marginal cost before they pay the fixed cost F and enter the market. After firm i enters market, it observes its constant marginal cost ci. (a) (5 points) Please write down the total cost function, average cost function, and marginal cost function of firm