(a) What is income elasticity of demand? The table below shows the various incomes and demand for different commodities. 

Income (N)	Quantity Demanded (kg)
A    20,000	120
B    36,000	96
C    40,000	160
D    44,000	200
E    45,000	240
F    47,000	252

(b) Calculate the income elasticity between
(i) A and B
(ii) C and D
(iii) E and F
(c) What kind of good is between
(i) A and B?
(ii) C and D?