If $a \clubsuit b = a^2 + 2ab + b^2$ and $2 \clubsuit x = 81$, find the sum of all possible values of $x$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $a \clubsuit b = a^2 + 2ab + b^2$ and $2 \clubsuit x = 81$, find the sum of all possible values of $x$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-4
If $a \clubsuit b = a^2 + 2ab + b^2$ and $2 \clubsuit x = 81$, find the sum of all possible values of $x$.
train