A Lawn Service Is Deciding Whether to Add an Additional

A lawn service is deciding whether to add an additional employee to its summer crew. The marginal cost of hiring this worker depends on the

A) the total amount paid to all the workers, both the new one and the previously hired workers.
B) total amount paid to only the new worker.
C) total amount paid to all previously hired workers.
D) the additional revenue created by having an additional worker minus the cost of hiring the worker.