Stone age surfboards is a small manufacturer of two types of popular high-tide surfboards, the rockwell and the limestone models. the manufacturing process consists of two departments: fabrication and finishing. the fabrication department has 15 skilled workers, each of whom works 5 hours per day. the finishing department has 5 workers, who also work a 5-hour shift. each pair of rockwell surfboards requires 3 labor hours in the fabrication department and 1.5 labor hours in finishing. the limestone model requires 4.5 labor-hours in fabrication and 2 labor-hours in finishing. the company operates 6 days a week. it makes a per-unit profit of $60 on the rockwell model and $75 on the limestone model. approximately 4.1 rockwell models and 8.2 limestone models are produced per day. formulate an optimization problem to maximize the profit.