Answer
$f^{-1}(x)=\dfrac{x}{5} -0.4$
Work Step by Step
Replace $f(x)$ by $y$ to have:
$y=5x+2$
Interchange $x$ and $y$ then solve for $y$ to have:
$x = 5y+2
\\x-2= 5y
\\\dfrac{x-2}{5}=y
\\\dfrac{x}{5} -\dfrac{2}{5}=y
\\y=\dfrac{x}{5} -0.4$
Replace $y$ with $f^{-1}(x)$ to have:
$f^{-1}(x)=\dfrac{x}{5} -0.4$
