If 7x = 8k and 5y = 6k, then the value of ratio x is to y is :

$\frac{7 x}{5 y}=\frac{8 k}{6 k}=\frac{4 k}{3 k}$

$\Rightarrow \frac{x}{y}=\frac{20 k}{21 k}$

$\Rightarrow x: y=20: 21$