Here, f(x) = √x+9
g(x) = 8x - 13
So, for f(g(x)), just put the value of function g(x) in the function f(x)
It would be: f(g(x)) = √8x - 13 + 9
f(g(x)) = √8x - 4
Now, Take √4 as a common factor:
f(g(x)) = √4(√2x - 1)
f(g(x)) = 2(√2x - 1)
In short, Your Answer would be: f(g(x)) = 2(√2x - 1)
Hope this helps!