An electronics firm makes a clock radio in two different models: one (model 380 ) with a battery backup feature and the other (model 360 ) without. It takes 1 hour and 15 minutes to manufacture each unit of the model 380 radio, and only 1 hour to manufacture each unit of the model $360 .$ At least 500 units of the model 360 radio are to be produced. The manufacturer realizes a profit per radio of $\$ 15$ for the model 380 and only $\$ 10$ for the model $360 .$ If at most 2000 hours are to be allocated to the manufacture of the two models combined, how many of each model should be made to maximize the total profit?