Answer
$3\leq x$, $k^{-1}(x)=x+3$.
Work Step by Step
To make the function one-to-one, according to the graph, we can restrict its domain to $3\leq x$. If we want to get a formula for the inverse function, we swap $x$ and $y$ and solve for $y$. Hence, after swapping $x$ and $y$, we get:
$x=|y-3|\\x=y-3\\y=k^{-1}(x)=x+3$
