Suppose that each firm has the long run cost function c ( y ) = y 2+ 9 for y 0 and c (0) = 0. The industry demand is given by D ( p )= 51 - p .

22. Suppose that each firm has the long run cost function ​c​(​y​) = ​y​2​ + 9 for ​y​ > 0 and ​c​(0) = 0. The industry demand is given by ​D​(​p)​ = 51 - ​p​. The ​equilibrium price ​in the long-run equilibrium of the industry in a perfectly competitive market is:

a. $8 b. $3 c. $5 d. $4 e. $6