A company produces two products (A and B) using three resources (I, II, and III). Each product A requires 1 unit of resource I and 3 units of resource II; and has a profit of $1. Each product B requires 2 units of resource I, 3 units of resource II, and 4 units of resource III; and has a profit of $3. Resource I is constrained to 40 units maximum per day; resource II, 90 units; and resource III, 60 units. What is the objective function?