Machines A and B produce bottles at their respective constant rates

Machines A and B produce bottles at their respective constant rates. Machine A produces k bottles in 3 hours and machine B produces k bottles in 5 hours. How many hours does it take machines A and B, working simultaneously, to produce 16k bottles?

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 #5891