\(\Leftrightarrow\hept{\begin{cases}6x-5y=0\\8y-4z=0\\2x+y-z-4=0\end{cases}}\)\(\Leftrightarrow\hept{\begin{cases}6x=5y\\2y=z\\2x+y-z=4\end{cases}}\)\(\Leftrightarrow\hept{\begin{cases}\frac{x}{5}=\frac{y}{6}=\frac{z}{12}\\2x+y-z=4\end{cases}}\)
\(\Leftrightarrow\frac{x}{5}=\frac{y}{6}=\frac{z}{12}=\frac{2x+y-z}{10+6-12}=\frac{4}{4}=1\)
\(\Rightarrow x=5\)
\(y=6\)
\(z=12\)