Question: The LaCrosse Iron Works makes two models of cast-iron fireplace grates, model A and model B. Producing one model-A grate requires 20 lb of cast iron and 20 min of labor, whereas producing one model-B grate requires 30 lb of cast iron and 15 min of labor. The profit for a model-A grate is $6, and the profit for a model-B grate is $8. There are 7200 lb of cast iron and 100 labor-hours available each week. Because of a surplus from the previous week, the proprietor has decided that he should make no more than 150 units of model-A grates this week. Determine how many of each model he should make in order to maximize his profit.