Suppose the marginal expense of hiring another worker is $150, and the marginal expense of hiring current workers

Suppose the marginal expense of hiring another worker is $150, and the marginal expense of hiring current workers

for an extra hour is $10. The added output associated with an added worker, holding both capital and average hours per worker constant, is 120. The added output generated by increasing average hours per worker, holding capital and the number of employees constant, is 7. If the firm is interested in maximizing profits, what should it do?