The demand curve and marginal benefit curve for paint is (see Chapter 6 , here ). The supply curve and marginal private cost curve of producers of the paint is (see Chapter 6 , here ). The supply curve is the marginal private cost curve because when firms make their supply decisions, they pursue their self-interest and consider only the costs that they will bear. The market equilibrium occurs where marginal benefit equals marginal private cost. The price is $1.00 a gallon and the quantity is 4 million gallons of paint a month. This outcome is inefficient