Answer
$2$
Work Step by Step
If $f$ has an inverse, and $f(a)=b$
then $f^{-1}(b)=a.$
The table gives us $f(6)=1,$ so $f^{-1}(1)=6$
Also, the table gives us $f(2)=6,$ so $f^{-1}(6)=2$
Thus
$f^{-1}(f^{-1}(1))=f^{-1}(6)=2$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.