The demand for good X is estimated to be Qx
d = 10, 000 - 4PX + 5PY + 2M + AX, where PX is
the price of X, PY is the price of good Y, M is income and AX is the amount of advertising on X. Suppose the present price of good X is $50, PY = $100, M = $25,000, and AX = 1,000 units. Based on this information, the income elasticity of good X is?