\(\Leftrightarrow\left\{{}\begin{matrix}60\left(\dfrac{3}{4}x-\dfrac{1}{5}y\right)=4\\60\left(\dfrac{2}{3}x+\dfrac{4}{5}y\right)=120\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}45x-12y=4\\40x+48y=120\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}180x-48y=16\\40x+48y=120\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}220x=136\\45x-12y=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{34}{55}\\y=\dfrac{131}{66}\end{matrix}\right.\)
\(\left\{{}\begin{matrix}\dfrac{3}{4}x-\dfrac{1}{5}y=\dfrac{1}{15}.\\\dfrac{2}{3}x+\dfrac{4}{5}y=2.\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}3x-\dfrac{4}{5}y=\dfrac{4}{15}.\\\dfrac{2}{3}x+\dfrac{4}{5}y=2.\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{11}{3}x=\dfrac{34}{15}.\\\dfrac{2}{3}x+\dfrac{4}{5}y=2.\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{34}{55}.\\y=\dfrac{131}{66}.\end{matrix}\right.\)
