The current in a river is 3 mph

The current in a river is 3 mph. A boat can travel 21 mph in still water. How far up the river can the boat travel if the round trip is to take 10 hours?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #16721