For our simple model, suppose that the quantity of regular beer demanded per year (Q) is a function of the price of regular beer (p), the price of premium beer (p’), the temperature (t), and the income of consumers (Y): Q = D (p, p’, t, Y). Quantity demanded is in billions of 2.25- gallon cases and prices are per 2.25-gallon case. Specifically, assume that the demand function for regular beer is: