Working individually, Amy can hang picture frames for 5 hours and John…

Working individually, Amy can hang picture frames for 5 hours and John can hang picture frames in 4 hours. If Amy and John work together but independently at the task for 1 hour, at which point John leaves, how many remaining hours will it take Amy to complete the task alone?

Its source gives only the correct option, without the working.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #92779