I still don't understand this. What's the answer? I don't know what to do on this problem. Does someone have the answer?
A retailer plans to sell two models of high-quality headphones. The retailer can purchase the wired model for $350 and the wireless model for $400. The wired model yields a profit of $85 and the wireless model yields a profit of $90. The total demand per month for the two models will not exceed 150. The retailer can invest no more than $56,000 for inventory of these items. Find the number of each model that should be stocked each month in order to maximize the retailer's profit.