[tex]\it \dfrac{x}{11}=\dfrac{y}{9}=\dfrac{z}{3}=k\ \ \ \ \ (1)\\ \\ \\ \dfrac{x}{11}+\dfrac{y}{9}+\dfrac{z}{3}=18\ \stackrel{(1)}{\Longrightarrow} k+k+k=18 \Rightarrow 3k=18|_{:3} \Rightarrow k=6\ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow \begin{cases} \it \dfrac{x}{11}=6 \Rightarrow x=11\cdot6=66\\ \\ \it \dfrac{y}{9}=6 \Rightarrow y=9\cdot6=54\end{cases}[/tex]
