Suppose the own price elasticity of demand for good X is -3, its income elasticity is 1, its advertising elasticity is 2, and the cross-price elasticity of demand between it and good Y is -4

a) Increase by 15%. Quantity demanded increases when price falls since own price elasticity is negative. With a price elasticity of 3, quantity demanded will increase by (3 x 5) = 15% when price drops by 5%.

b) Decrease by 32%. Quantity demanded for good X decreases when price of good Y increases since cross-price elasticity is negative. With a cross-price elasticity of -4, quantity demanded will decrease by (4 x 8) = 32% when price of good Y increases by 8%.

c) Decrease by 8%. Quantity demanded decreases when advertising falls since advertising elasticity is positive. With a advertising elasticity of 2, quantity demanded will increase by (2 x 4) = 8% when advertising drops by 4%.

d) Increase by 4%. Quantity demanded increases when income rises since income elasticity is positive. With an income elasticity of 1, quantity demanded will increase by (1 x 4) = 4% when income increases by 4%.