(a) Define cross elasticity of demand.
(b) The table below shows the response of quantity demanded to changes in price for three pairs of commodities.
Use the table to answer the questions that follow. 

Commodity	changes in price		commodity	Changes in Quantity Demanded
	Original Price (N)	New price (N)		Original Quantity (kg)	New Quantity (kg)
Bread	15	20	Yam	150	200
Beef	25	40	Fish	1,000	3,000
Butter	100	50	Margarine	250	400