Answer
$x$
Work Step by Step
We know that $F(x)=1/(x-3)$, so:
$F(\frac{3x+1}{x})=F(3+1/x)=1/(3+1/x-3)=1/(1/x)=x$
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.