The Cheese Business in Lake Fon-Du-Lac, Wisconsin, Is a Competitive

The cheese business in Lake Fon-du-lac, Wisconsin, is a competitive industry. All cheese manufacturers have the cost function C = Q² + 4, while demand for cheese in the town is given by Q_d = 120 - P. The long-run equilibrium number of firms in this industry is

A) 29.
B) 58.
C) 56.
D) 120.
E) 59.