Answer
$f^{-1}(x)=\frac{x}{3x-2}$
Work Step by Step
$f(x)=\frac{2x}{3x-1},$
$y=\frac{2x}{3x-1},$
a. $x=\frac{2y}{3y-1},$
$x(3y-1)=2y,$
$3xy-x=2y,$
$3xy-2y=x,$
$y(3x-2)=x,$
$y=\frac{x}{3x-2}=f^{-1}(x),$
b.Domain of $f(x)$ is $x\in \mathbb{R} \ne \frac{1}{3},$ and Domain of $f^{-1}(x)$ is $x\in \mathbb{R} \ne \frac{2}{3}$