jmc

We can see that $2♣x=2^2+2\cdot 2\cdot x+x^2=81$. This becomes a quadratic: $x^2+4x-77=(x+11)(x-7)=0$. Thus, $x=7,-11$ and our answer is $\boxed{-4}$.

- OR -

We note that $a♣b=(a+b{)}^2$. Thus, $(2+x{)}^2=81$. It follows that $2+x=9$ or $2+x=-9$, leaving us with $x=7,-11$. We find that the answer is $\boxed{-4}$.