If $f(x)=g(g(x))-g(x)$ and $g(x)=2x-1$, find $f(3)$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $f(x)=g(g(x))-g(x)$ and $g(x)=2x-1$, find $f(3)$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
4
If $f(x)=g(g(x))-g(x)$ and $g(x)=2x-1$, find $f(3)$.
train