3. Let the market demand for a perfectly competitive industry is QD= 800-2P. Let industry supply be QS= -100+10P. Each firm has a total cost function C(q)=(37.5)q^2+37.5. The firm's output is denoted by q. Find its optimal output and level of profits. Is this a long run equilibrium? Why or why not?

4. Suppose that a firm's production function is Q=KL, where K=2. Draw (graph) the total product of labor, marginal product of labor, average product of labor, total cost, total variable cost, marginal cost, average variable cost, average fixed cost, and average total cost.