Data on price of Y, quantity demand for X when income is 100, and quantity demand for X when income is 200 are given in the following table. The price of X is fixed at $7.

Py QDx (Income $100) QDx (Income $200)

0 121.5 196.5

1 120.2 195.2

2 118.9 193.9

3 117.6 192.6

4 116.3 191.3

5 115 190

6 113.7 188.7

7 112.4 187.4

8 111.1 186.1

9 109.8 184.8

10 108.5 183.5

a. Calculate income elasticity of demand for X using the midpoint method when income increases from $100 to $200 and when price of Y is fixed at $9. Explain your answer.

b. Calculate cross price elasticity of demand for X when price of Y decreases from $9 to $8 and when income is $100. Explain your answer.