\(\left\{{}\begin{matrix}p+n+e=25\\p+e-n=7\\p=e\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}2p+n=25\\2p-n=7\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}2p=\left(25+7\right):2=16\\n=25-16=9\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}p=8\\e=8\\n=9\end{matrix}\right.\)