solution: Rewrite $4$ as $2^2$ to find $4^x=2^{2x}$.  Since $2^8=2^{2x}$, we have $2x=8$ which implies $x=\boxed{4}$.
prompt.content: <|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
  
prompt.role: user
extra_info.answer: 4
extra_info.question: If $2^8=4^x$, what is the value of $x$?
extra_info.split: test