Taxi drivers, whose income is based on the fares they receive, usually decide when to finish work each day by setting a daily income target; they stop when they reach that target.
Facts
Taxi drivers decide on a certain total amount of money they want to work in a day (say, $150), and then as soon as they hit that amount, they stop working. Because of this, they typically work fewer hours on a busy day than a slow day.
Evaluation
When we see causal connector language -- due to, because of, this means that, this makes possible, this allows for, etc -- we usually see correct answers reinforcing the causal relationship. And when we're presented with two mathematical ideas, the correct answer usually involves what can be inferred by combining those two math ideas.
So, if we know that on busy days they take fewer hours to reach amount X, and on slow days they take more hours to reach amount X, then on busy days they are earning more money per hour.
Goal
Since we want to go against the passage, look for an answer saying that busy days have better hourly revenue than do slow days.