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 $P = 60 - Q$ , 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.