Ta có:
\(\left\{{}\begin{matrix}p+e+n=58\\p+e-n=18\\p=e=z\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2z=58-n\\2z=18+n\\p=e=z\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2z=58-n=18+n\\p=e=z\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2n=40\\p=e=z=\frac{58-n}{2}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}n=20\\p=e=z=17\end{matrix}\right.\)
Ta có \(A=z+n=17+20=37\)