Out of four numbers ,the average of first three is 20 and…

Out of four numbers ,the average of first three is 20 and that of the last three is 15. If the last number is 18,the first number is :

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 #33189