The average age of 39 students in a group is 14 years

The average age of 39 students in a group is 14 years. When teacher's age is included to it, the average increases by one. What is the teacher's age in years ?

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 #37672