12. The marginal benet and marginal private cost curves for aphrodisiacs are given as follows: MB = 200 Q, MPC = Q. In addition to private costs, there is a marginal external cost of $10 per unit of output. What is the efcient level of output? (a) 0 (b) 55 (c) 95 (d) 100 (e) none of the above 13. A third-degree price (liscrin'iinating monopolist can sell its output either in the local market or on an internet auction site (or both). After selling all of its output. the rm discovers that the marginal revenue earned in the local market was $20 while its marginal revenue on the internet auction site was $30. To maximize prots the firm should (a) have sold more output in the local market and less at the internet auction site. (b) do nothing until it acquires more information on costs. (c) have sold less output in the local market and more on the internet auction site. ((1) sell less in both markets until marginal revenue is zero. (e) sell more in both markets until marginal cost is zero