$a)\frac{x}{y}=\frac{-2}{10}$

$10x=-2y\mid :\left(-2\right)$

$y=-5x$

 

$b)\frac{x}{y}=\frac{6}{-4}$

$-4x=6y\mid :6$

$y=-\frac{4}{6}x=-\frac{2}{3}x$

 

$c)\frac{x}{y}=\frac{8}{2}$

$2x=8y\mid :8$

$y=\frac{2}{8}x=\frac{1}{4}x$