17
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
The lengths of the three sides of a triangle are $7$, $x+4$ and $2x+1$.  The perimeter of the triangle is 36.  What is the length of the longest side of the triangle?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
17
The lengths of the three sides of a triangle are $7$, $x+4$ and $2x+1$.  The perimeter of the triangle is 36.  What is the length of the longest side of the triangle?
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