Profit-maximizing firms must determine how hiring an additional unit of labor will affect profit. To do this, the firm can compare the change in revenue from hiring an additional unit of labor against the cost of that extra worker. The additional output produced by an extra unit of labor is equal to the marginal product of labor (MPL). Because each bot sells for the market price (P), the change in revenue from hiring an additional worker is________and the change in cost is_______.