the only of production. In this case the marginal cost of producing an additional unit of output was the money wage(wy, the amount paid for an additional unit of labor, by the marginal product of labor Marginal cost(WIMPN) increased as output increased because as more labor was hire the marginal product of labor(MPN) declined. In addition, the variable-wage model of the preceding section, in order for workers to supply additional labor, the money wage had to be increased, a further factor causing marginal cost to rise as output increased. These two factors, the declining marginal