The respective ages of father and his son are 40 and 16…

The respective ages of father and his son are 40 and 16 years. In how many years will the father be twice as old as his son ?

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 #3142