The average of 13 result is 20

The average of 13 result is 20. Average of the first 8 of them is 20 and that of the last 8 is 40. Find the 8th result?

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 #2802