A dual sink has a right side and left side

A dual sink has a right side and left side. Working alone, the right side can fill up in 5 hours. Working alone, the left side can empty in 15 hours. If it is desired that the sink should be filled, from empty, exactly 6 hours after the right side is turned on at 9:30am, then at what time should the left side also be turned on?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #18224