Pipe A can fill a tank in 60 min

Pipe A can fill a tank in 60 min . There is a second pipe in the bottom of the cistern to empty it. If all the two pipes are simultaneously opened, then the cistern is full in 180 min. In how much time, the second pipe alone can empty the cistern?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #60120