pls show steps

$\frac{y-2}{y^2 - 9} - \frac{y-7}{y^2 + 4y - 21}$

$\frac{y-2}{(y+3)(y-3)} - \frac{y-7}{(y+7)(y-3)}$

$\frac{(y+7)(y-2) - (y+3)(y-7)}{(y+3)(y-3)(y+7)}$

$\frac{(y^2 + 5y - 14) - (y^2 - 4y - 21)}{(y+3)(y-3)(y+7)}$

$\frac{y+7}{(y+3)(y-3)(y+7)}$

$\boxed{\frac{1}{(y+3)(y-3)}}$

Excuse the handwriting..

Hmmm, I got something similar to what Log got...

$\frac{y-2}{y^2\:-\:9}\:-\:\frac{y-7}{y^2\:+\:4y\:-\:21}$

$=\frac{y-2}{\left(y+3\right)\left(y-3\right)}-\frac{y-7}{y^2+4y-21}$

$=\frac{y-2}{\left(y+3\right)\left(y-3\right)}-\frac{y-7}{\left(y-3\right)\left(y+7\right)}$

$=\frac{\left(y-2\right)\left(y+7\right)}{\left(y+3\right)\left(y-3\right)\left(y+7\right)}-\frac{\left(y-7\right)\left(y+3\right)}{\left(y-3\right)\left(y+7\right)\left(y+3\right)}$

$=\frac{\left(y-2\right)\left(y+7\right)-\left(y-7\right)\left(y+3\right)}{\left(y+3\right)\left(y-3\right)\left(y+7\right)}$

$=\frac{9y+7}{\left(y+3\right)\left(y-3\right)\left(y+7\right)}$