HYT is a retailer selling a new cellphone with a customer demand given by D(p) = 1800 - 25*p, where p is the selling price. It now has a wholesale price contract with its supplier POY, with a wholesale price w = 30. The cellphone has a manufacturing cost of c=20 (All quantities are measured in hundreds of HKD). a) What is the optimal selling price for the entire supply chain, i.e., maximizing the total profit of HYT and POY? [5pts]