Two pipes can fill a tank in 15 hours and 30 hours

Two pipes can fill a tank in 15 hours and 30 hours. While the 3rd pipe empties the full tank in 45hours. If all the 3 pipes are open in how much time will the tank be filled?

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 #24696