The total revenue for a product can be calculated as the area under the demand curve. Suppose that the demand curve for a certain wine (in dollars per liter) is given by the following, where q is the demand in liters. Estimate the total revenue using rectangles of width 10 liters. D(q) = - 1 109 -10q+ 280 for O s q s 50 . . . The approximate revenue using left endpoints is $