\(\left\{{}\begin{matrix}P=E\\\dfrac{P+E}{N}=\dfrac{16}{9}\\\left(P+N\right)-E=9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}P-E=0\\9.2P-16N=0\\P+N-E=9\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=8\\E=8\\N=9\end{matrix}\right.\\ \Rightarrow A=P+N=8+9=17\left(đ.v.C\right)\)