Answer
$f^{-1}(x)=3(x+5)$
Work Step by Step
Given: $y=\dfrac{1}{3}x-5$
Also, $f(x)=\dfrac{1}{3}x-5$
In order to find the inverse will have to interchange the variables such as: $x=\dfrac{1}{3}y-5$
or, $x+5=\dfrac{1}{3}y$
or, $3(x+5)=y$
Hence, $f^{-1}(x)=3(x+5)$
