Final answer:
The formula MPl / MPk = W / C is used in microeconomics to represent the optimal balance of labor and capital for a firm, where the cost of each input equals the marginal product.
Step-by-step explanation:
The formula MPl / MPk = W / C represents the equalization of the ratio of the marginal products of labor (MPl) to the marginal products of capital (MPk) to the ratio of the wage rate (W) to the cost of capital (C) in microeconomics, particularly in the study of production theory and firm behavior. This formula illustrates the condition under which a firm has balanced its input usage to minimize cost and maximize efficiency. If this equality holds, the firm is said to be optimizing its use of labor and capital, such that the last dollar spent on each input yields the same marginal product, which is a foundational concept in the theory of the firm and analysis of production costs.