Restricting the Domain to Find the Inverse of a Polynomial Function

Find the inverse function of $f:$

ⓐ $f\left(x\right)={\left(x-4\right)}^2,x\ge 4$
ⓑ $f\left(x\right)={\left(x-4\right)}^2,x\le 4$

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Algebra and Trigonometry 2e · §5.7 Inverses and Radical Functions · Example 6