Từ \(\hept{\begin{cases}3x=y\\5y=4z\end{cases}\Rightarrow\hept{\begin{cases}\frac{x}{1}=\frac{y}{3}\\\frac{y}{4}=\frac{z}{5}\end{cases}\Rightarrow}\hept{\begin{cases}\frac{x}{4}=\frac{y}{12}\\\frac{y}{12}=\frac{z}{15}\end{cases}\Rightarrow}\frac{x}{4}=\frac{y}{12}=\frac{z}{15}\Rightarrow\frac{6x}{24}=\frac{7y}{84}=\frac{8z}{120}=\frac{6x+7y+8z}{24+84+120}}\)
\(=\frac{456}{228}=2\)
=> x = 8 ; y = 24 ; z = 30