Suppose that the inverse demand curve for paper is ( = 200 - Q, the private marginal

Question:

Suppose that the inverse demand curve for paper is ( = 200 - Q, the private marginal cost (unregulated competitive market supply) is MC( = 80 + Q, and the marginal harm from gunk is MCg = Q.
a. What is the unregulated competitive equilibrium?
b. What is the social optimum?
c. What specific tax (per unit of output of gunk) results in the social optimum?