Answer
We find the relation
$g'[f(x)]\cdot f'(x)=1$
Work Step by Step
$(g\circ f)(x)=x$
$g[f(x)]=x$
... differentiating both sides
$\displaystyle \frac{d}{dx}\{g[f(x)]\}=\frac{d}{dx}[x]$
... using the chain rule
$g'[f(x)]\cdot f'(x)=1$