Assume the marginal product of labor is MPL = 20 and the marginal product of capital is MPK = 50. In addition, the price of labor is wL = 10 and the price of capital is wK = 30. Then, if a manger wants to lower the costs of production, the manager should use
a) An equal number of workers and machines
b) More workers and more machines
c) More machines and fewer workers
d) More workers and fewer machines