The marginal social cost (MSC) of an electricity generating plant that uses coal is estimated by a consulting firm to be MSC=3Q, where Q is the output. The consulting firm also provides an estimate of the supply schedule. The marginal private cost (MPC) is estimated to be MPC=Q. The demand is estimated to be P=60-2Q.

a) Given these estimates, what is the impact of the externality? How large is the over- or underproduction? What is the socially optimal price? Is there over- or under-pricing?