Answer
$f^{-1} (x)=y=\dfrac{4x-40}{3}$
Work Step by Step
Let $x$ be wages and $y$ be the number of units produced.
We have $y=10+0.75 x$
To compute the inverse, we will have to interchange $x$ and $y$.
$x=10+0.75 y$
Re-write as: $ y=\dfrac{4x-40}{3}$
Replace $y$ with $f^{-1} (x)$.
So, the inverse function is: $f^{-1} (x)=y=\dfrac{4x-40}{3}$
