\(\left\{{}\begin{matrix}\frac{x}{5}=\frac{z}{3}\Rightarrow z=\frac{3}{5}x\\\frac{x}{5}=\frac{y}{7}\Rightarrow y=\frac{7}{5}x\end{matrix}\right.\) thay vào pt dưới:
\(2x-\frac{7}{5}x+4.\frac{3}{5}x=30\)
\(\Leftrightarrow3x=30\Rightarrow x=10\)
\(\Rightarrow y=\frac{7}{5}x=14\); \(z=\frac{3}{5}x=6\)