Q3 [40 points] Draw a set of indifference curves showing utility levels U = 6, U = 8, and U = 12 for each of the utility functions below. You must show all your calculations. [Calculations: 25 points, Curves; 5 points] a) U= XY b) U = X +Y c) U= X-Y d) Are the commodities in the utility function given by (b) complements? Substitutes? Explain. e) What about the commodities in the utility function given by (c)? Explain