I believe it's the first option. Hope this helps.
Answer:
The function is 
Step-by-step explanation:
Given : If
and 
To find : The function f(x) ?
Solution :
where the function g is inside of the function f.
We have given,

The function 
Substitute in equation,

We know that g(x) is placed over x in the function,

Therefore, The function is 