Answer:
A perfectly competitive industry is an industry in which the number of buyers and sellers is very large, none large enough to influence the industry and are all engaged in buying and selling of a homogeneous product. In perfect competition, equilibrium is the point where market demands equals market supply. A firm's price is determined at this point. In the short run, equilibrium will be affected by demand. In the long run, both demand and supply of a product will affect the equilibrium in perfect competition.
In constant-cost industry, where the equilibrium price is $56 and the minimum average total cost of the industry's firms is $40, we can expect that in the long run, firms will enter the market, shifting the industry's short-run supply curve outward until the new equilibrium price is $40.