Clear voice faces 100 high-demand consumers, whose demand function is QH = 150 - 100PH, and 400

Question:

Clear voice faces 100 high-demand consumers, whose demand function is QH = 150 - 100PH, and 400 low-demand consumers, whose demand function is QL = 50 - 100PL. It has a marginal cost of 10 cents per minute. What is its profit-maximizing two-part tariff?