since, we are given a parent function f(x) as: f(x)=x.
We are asked to find what change will occur in the function when the parent function f(x) is replaced by f(9x).
let g(x) be the function formed by replacing f(x) with f(9x) i.e.
g(x)=f(9x)=9x.
clearly the slope of the function g(x)=f(9x) is 9. ( since on comparing the equation with the slope intercept form y=mx+c; where m is the slope of the line and c is the y- intercept).
whereas the slope of the function f(x)=x is 1.
Hence there is an increment of slope by a factor of 9.