\(\hept{\begin{cases}\frac{9x}{7}-\frac{2y}{3}=-28\\\frac{3x}{2}+\frac{12y}{5}=15\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}27x-14y=-588\\15x+24y=150\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}135x-70y=-2940\\135x+216y=1350\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}135x-70y-135x-216y=-2940-1350\\135x+216y=1350\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}-286y=-4290\\135x+216y=1350\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}y=15\\135x+216y=1350\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}x=-14\\y=15\end{cases}}\)