a firm that produces medicine sells its cough medicine in two cities, a and b. the demand functions in these two cities, respectively, are: pa = 18-qa and pb = 14- qb. the firm's plant is located roughly midway between the two cities. as a result, the total cost of producing and delivering cough medicine to each town is: 2 + 3q; where i = a, b. (3 marks) compute the optimal price of the firm's cough medicine if the two cities are treated as a common market