Suppose That an Industry Emits a Chemical That Pollutes the Ground

Suppose that an industry emits a chemical that pollutes the ground water.Without considering the effects of the pollution,the industry has a marginal private cost curve of MPC = Q+30.The market demand curve is ,while the marginal social cost curve is MSC = 2Q + 30.What is the socially optimal emissions standard?

A) 15.
B) 10.
C) 5.
D) 0.