If the marginal social benefit of a lighthouse is \$30 and the marginal social cost is \$30, what is the optimal quantity of the lighthouse service?

• A. The quantity where marginal social benefit equals marginal social cost.
• B. The quantity where marginal social benefit is greater than marginal social cost.
• C. The quantity where marginal social benefit is zero.
• D. The quantity where marginal social cost is greater than marginal social benefit.

Answer: (A)