Rewrite $4$ as $2^2$ to find $4^x=2^{2x}$.  Since $2^8=2^{2x}$, we have $2x=8$ which implies $x=\boxed{4}$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $2^8=4^x$, what is the value of $x$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
4
If $2^8=4^x$, what is the value of $x$?
test