An Environmental Economic Consulting Firm Is Hired to Measure the Negative

An environmental economic consulting firm is hired to measure the negative externalities associated with the pollution from an industry. The marginal social cost production can be expressed as MSC = 2Q + 30. The consultants calculate the marginal private cost production to be MPC = Q+30. The market demand curve can be expressed as $P = 60 - Q$ . If the consultants have accurately measured the impact of the pollution externality, the $\underline{\text{change}}$ in social surplus from moving to the social optimum (rather than at the private optimum) is

A) $30
B) $37.5.
C) $55.
D) $67.5.