<P> In economics, profit maximization is the short run or long run process by which a firm determines the price and output level that returns the greatest profit . There are several approaches to this problem . The total revenue--total cost perspective relies on the fact that revenue equals profit minus cost and focuses on maximizing this difference, and the marginal revenue--marginal cost perspective is based on the fact that total profit reaches its maximum point where marginal revenue equals marginal cost . </P> <P> Any costs incurred by a firm may be classed into three groups: fixed costs and variable costs . Fixed costs, which occur only in the short run, are incurred by the business at any level of output, including zero output . These may include equipment maintenance, rent, wages of employees whose numbers cannot be increased or decreased in the short run, and general upkeep . Variable costs change with the level of output, increasing as more product is generated . Materials consumed during production often have the largest impact on this category, which also includes the wages of employees who can be hired and laid off in the span of time (long run or short run) under consideration . Fixed cost and variable cost, combined, equal total cost . </P>

Profit-maximizing firms want to maximize the difference between