Demand for phones at Amazon is 5,000 per month. The holding cost at Amazon is 25 percent and the company incurs a fixed cost of $500 for each order placed. The supplier offers an all unit quanitity discount with a price of $200 per phone for all orders under 10,000, a price of $195 for all orders of 10,000 or more but under 20,000 and a price of $190 for all orders of 20,000 or more. How many phones should Amazon order per replenishment? Please show work!