Ta có 7x = 9y \(\Rightarrow\frac{x}{9}=\frac{y}{7}\Rightarrow\frac{10.x}{10.9}=\frac{8.y}{8.7}\Rightarrow\frac{10x}{90}=\frac{8y}{56}=\frac{10x-8y}{90-56}=\frac{68}{34}=2\)
Vậy \(\frac{10x}{90}=2\Rightarrow\frac{x}{9}=2\Rightarrow x=18\)
\(\frac{8y}{56}=2\Rightarrow\frac{y}{7}=2\Rightarrow y=14\)