A market contains many identical firms, each with the short run total cost function STC(Q) = 400 + 5Q + Q 2 , where Q is the firm's annual output (and all of the firm's $400 fixed cost is sunk). The...

A market contains many identical firms, each with the short run total cost function STC(Q) = 400 + 5Q + Q², where Q is the firm's annual output (and all of the firm's $400 fixed cost is sunk).

The market demand curve for this industry is Q = 262.5 - P/2, where P is the market price. Each firm in the industry is currently earning zero economic profit.

How many firms are in the industry and what is the market equilibrium price?