Suppose that the estimated demand equation for a firm’s good is Qx = 100 −10Px − 2Py + 0.1M + 0.2A, where Qx d is unit sales of good x, Px is the price of good x, Py is the price of good y, M is per-family money income in thousands of dollars, and A is the level of advertising expenditures in thousands of dollars.

Suppose that Px = $2, Py = $3, M = $50 (thousand), and A = $20

(thousand). Calculate the price elasticity of demand.