We want a function [tex]g[/tex] such that [tex]g(15x-1)=x[/tex]
One easy way to do to that is to choose [tex]g(x)=\dfrac{x+1}{15}[/tex]
That function works : [tex]g(15x-1)=\dfrac{15x-1+1}{15}=x[/tex]
Due to the uniqueness of the inverse, this is the function we were searching for.