The average of 11 numbers is 12.9

The average of 11 numbers is 12.9. If the average of first six is 12.5 and that of the last six is 11.4 the sixth 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 #82917