A competitive firm sells its output for $45 per unit. It employs 30 workers, and the marginal product of the 30th worker is four units of output per day. It pays its workers a wage of $150 per day. What will help the firm make the right decision regarding hiring a 31st worker?

For the 30th worker, the value of the marginal product of labour is $600 or for the 30th worker, the marginal revenue product is $600