Answer
$$y=\frac{x+1}{2}$$
Work Step by Step
Switching the elements of the domain and the range (in other words, the dependent and independent variables), we find that the inverse is:
$$x=2y-1 \\ y=\frac{x+1}{2}$$
Note, if we plug the inverse into the original function or the original function into the inverse, we should get x.