\(\left\{{}\begin{matrix}mn=\left(m+2\right)\left(n-2\right)\\mn=\left(m-2\right)\left(n+10\right)\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}mn-2m+2n-4=mn\\mn+10m-2n-20=mn\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}2m-2n+4=0\\10m-2n-20=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}8m-24=0\\n=m+2\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}m=3\\n=5\end{matrix}\right.\)

The answer is : 3 x 5 = 15