Average of 17 results is 71

Average of 17 results is 71. If the average of first eight results is 72 and average of last eight results is 69 Then find the ninth result?

Its source gives only the correct option, without the working.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #69447