Explanation

Imagining a case here helps understand the question even if we don't compute everything. The first hour costs more than the others - say it costs double. In that case, a 10-hour job, where , costs If we break it up into five jobs, two hours each it's . We can tell that it's going up, and that it depends on the number of jobs we are breaking it into, so (C) is the only possibility. We can, optionally, compute the difference in our case: . This corresponds to answer choice (C).

The correct answer is (C).