So, total profits are given by profits-per-unit (price minus average cost) times the number of units sold. Geometrically, profits unit are shown in figure 9-4 by the vertical distance EF. Notice that the average cost used to calculate these per unit is the actual average cost experienced when the firm produces q*. now , total profits are found by multiplying this vertical distance by the number of units sold, q* . these are therefore given by the area of the rectangle p* EPA. In this case, these profits are positive because P > SAC. These could be zero if P = SAC, of even negative if P< SAC. Regardless of whether profits are positive or negative, we know that they are as large as possible because output level q* obeys the marginal-revenue-equals-marginal-cost rule.⁵