Elasticity III

Consider the markets for mobile and landline telephone service. Suppose that when the average income of residents of Plainville is $55,000 per year, the quantity demanded of landline telephone service is 13,500 and the quantity demanded of mobile service is 29,000. Suppose that when the price of mobile service rises from $100 to $120 per month, the quantity demanded of landline service increases to 15,000. Suppose also that when the average income decreases to $50,000, the quantity demanded of mobile service decreases to 26,000.

What is the income elasticity of demand for mobile service? Show calculation and interpret the result.