Derive the demand functions from the utility function U = f ( q_1, q_{2, .........}q_n) subject to budget constraint and  y = p₁ q₁ + p₂ q₂  + ................q_n   if the demand function for a commodity i (i = 1, 2, ... n) is homogeneous of degree zero in prices and income, then show that the sum of own and cross price elasticities of demand for the commodity equals its income elasticity of demand with negative sign.  (15 Marks) (200 words)