Non-liquid assets could perform which of the following functions?

An economy's marginal social benefit curve for a private good is obtained by summing the individual marginal

a) cost curves horizontally b) benefit curves vertically c) benefit curves diagonally d) benefit curves horizontally

If a monopolist can sell 20 units at price of $200 per unit and 30 units at a price of $180 per unit, its marginal revenue at an output of 30 is

A) $-200. B) $800. C) $1400. D) $1800.