A man can do a piece of work in 15 days, but…

A man can do a piece of work in 15 days, but with the help of his son, he can do it in 6 days. In what time can the son do it alone?

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 #597