A retailer can obtain digital cameras from the manufacturer at a cost of $150 apiece. The retailer has been selling the cameras at the price of $340 apiece, and at this price, consumers have been buying 40 cameras a month. The retailer is planning to lower the prices to stimulate sales and estimates that for each $5 reduction in the price, 10 more cameras will be sold each month. Express the retailers monthly profit from the sale of the cameras as a function of the selling price. Estimate the optimal selling price.