2. Optimal choice and demand (40 pts) Always briey explain your answers! Yi has preferences over two goods, drinks with quantity d and dollars spent on food, f and has the utility function 2 u(f,d) = 3d+3f E The price per drink is $3 and Yi's income is m dollars. Call dollars spent on food good 1. (a) Explain that the price of good 1 (dollars spent on food) is p1 = $1 per unit. (b) Are the two goods perfect substitutes for Yi? Why or why not