\(\left\{{}\begin{matrix}2A+3G=3900\\G=900\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}A=T=600\left(nu\right)\\G=X=900\left(nu\right)\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}A=T=20\%N\\G=X=30\%N\end{matrix}\right.\)