121
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $\sqrt{400}=\sqrt{81}+\sqrt{n}$, then what is the value of $n$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
121
If $\sqrt{400}=\sqrt{81}+\sqrt{n}$, then what is the value of $n$?
train