Answers for A, B, C and D please

This question is about monopolistic competition and trade. Assume that firms in the automobile industry face the following price function P = 20000 + 2500 n where P is the equilibrium unit price a single firm demands and n denotes the number of firms that operate in the market. The average cost each firm faces is AC = 50000 . + 20000 where n denotes again the number of firms that operate in the market and S is the market size (i.e., the total number of automobiles that is produced). a) How do the price (P) and the average cost (AC) change if the number of firms increase? (2 pts) b) Assume that there is no trade and that the initial size of the automobile market in the US is 500 automobiles and in Japan it is 180 automobiles, respectively. Calculate (i) the equilibrium number of firms and (ii) the equilibrium price in the US. Provide intermediate steps of calculation. (5 pts) c) Now suppose that there is a free trade agreement so that the markets in the US and Japan become an integrated market of size S = 680. Calculate (i) the equilibrium number of firms and (ii) the equilibrium price in the integrated market. Provide intermediate steps of calculation. Round the number of firms to an integer. (5 pts) d) Usually firms differ with respect to their productivityes. How are firms with different productivityes affected if countries open for free trade? Briefly discuss. (3-6 sentences are expected) (3 pts)