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