A small community finds that tidy lawns and neighborhoods provide both private and external benefits. They determine the marginal private benefit (MPB) of lawns can be represented by the following equation: MPB = 50 – 0.5Q, where Q is the number of hours spent on keeping lawns tidy. The marginal private cost (MPC) of such lawn upkeep is represented by the following equation: MPC = 0.5Q, where Q is again the number of hours engaged in lawn upkeep.