Suppose that the monthly demand function for laptop computers is: QD = 10,000 40PL + .5I + 20PT where PL is the price of laptop computers, I is the annual per capita consumer income, and PT is the price of tablet computers. a. Express the quantity demanded of laptop computers as a function of the price of laptop computers (and only the price of laptop computers) when I = 40,000 and PT = 500. b. Graph the demand curve for laptop computers. Label it "D1." Represent QD on the horizontal axis in thousands computers. c. Suppose that PT decreases to 100. Derive the new demand function (QD = QD(PL)) and graph the new demand curve (label it "D2") on the same graph that you used in part (b) above.