\(\left\{{}\begin{matrix}2x+3y=66000\\x=63000-4y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2\left(63000-4y\right)+3y=66000\\x=63000-4y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}126000-8y+3y=66000\\x=63000-4y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-5y=-60000\\x=63000-4y\end{matrix}\right. \Leftrightarrow\left\{{}\begin{matrix}y=12000\\x=15000\end{matrix}\right.\)
\(\left\{{}\begin{matrix}2x+3y=66000\\x=63000-4y\end{matrix}\right.\Leftrightarrow}\left\{{}\begin{matrix}2.\left(63000-4y\right)+3y=66000\\x=63000-4y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}126000-8y+3y=66000\\x=63000-4y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-5y=-60000\\x=63000-4y\end{matrix}\right.\Leftrightarrow}}\left\{{}\begin{matrix}y=12000\\x=15000\end{matrix}\right.\)
