Short-run supply and long-run equilibrium Consider the competitive market for steel. Assume that, regardless of how many firms are in the industry, every firm in the industry is identical and faces the marginal cost (MC), average total cost (ATC), and average variable cost (AVC) curves shown on the following graph. 00 T 90 80 70 60 50 20, 30 40 ATC 30 20 10 5 10 15 20 25 30 35 40 45 50 QUANTITY Thousands of tons)