solution: We note that $361=19^2$ and $441=21^2$, so $x=21^2+2(21)(19)+19^2$. This is just the binomial expansion of $(21+19)^2=40^2=\boxed{1600}$.
prompt.content: <|im_start|>system
  You are a helpful assistant.<|im_end|>
  <|im_start|>user
  $441+2(21)(19)+361=x$. Solve for $x$.
  Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
  <|im_start|>assistant
  
prompt.role: user
extra_info.answer: 1600
extra_info.question: $441+2(21)(19)+361=x$. Solve for $x$.
extra_info.split: test