\(\left\{{}\begin{matrix}P+N+E=48\\P=E\\E:N=1:1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2E+N=48\\E=N\end{matrix}\right.\\ \Leftrightarrow3E=48\Leftrightarrow E=16\\ \Leftrightarrow\left\{{}\begin{matrix}P=16\\E=16\\N=16\end{matrix}\right.\)