An economy is composed of two individuals, whose demands for a public good – street lighting – are given by P = 12−(1/2)Q and P = 8−(1/3)Q. 

(a) Graph these demands on a diagram.

(b) Derive the total demand for this public good by summing the demands vertically, and write down a resulting equation for this demand curve. 

(c) Let the marginal cost of providing the good be $5 per unit. Find the efficient supply of the public good in this economy – where the marginal cost equals the total value of a marginal unit