\(\frac{y-2}{y^2 - 9} - \frac{y-7}{y^2 + 4y - 21}\)
\(\frac{y-2}{(y+3)(y-3)} - \frac{y-7}{(y+7)(y-3)}\)
\(\frac{(y+7)(y-2) - (y+3)(y-7)}{(y+3)(y-3)(y+7)}\)
\(\frac{(y^2 + 5y - 14) - (y^2 - 4y - 21)}{(y+3)(y-3)(y+7)}\)
\(\frac{y+7}{(y+3)(y-3)(y+7)}\)
\(\boxed{\frac{1}{(y+3)(y-3)}}\)
.