Tom decided to go on a trip. During this trip, he needs to cross a lake, which in one direction takes 4 hours. During this time, Tom needs an assistant to help him with the crossing. Hiring an assistant costs $10 per hour. How much would Tom have to pay for help with crossing the lake back and forth?
Reason slowly and give your answer.
80
Crossing the lake two times (back and forth) would take 4 * 2 = 8 hours.

So Tom would need to pay an assistant 8 * 10 = $80.

.

Thus, the answer is 80