You are an efficiency expert hired by a manufacturing firm that uses capital and labor as inputs. The firm produces and sells a given output and is currently employing 50 workers and 10 machines. During the consulting process, you find out that for this company capital is much more productive than labor: the marginal product of labor is 4 and the marginal product of capital is 50. The average wage rate they pay to their workers is $40 per hour, and the rental rate of capital is $100 per hour. The cost function for this firm is: