Hmmm, I got something similar to what Log got...
\(\frac{y-2}{y^2\:-\:9}\:-\:\frac{y-7}{y^2\:+\:4y\:-\:21}\)
\(=\frac{y-2}{\left(y+3\right)\left(y-3\right)}-\frac{y-7}{y^2+4y-21}\)
\(=\frac{y-2}{\left(y+3\right)\left(y-3\right)}-\frac{y-7}{\left(y-3\right)\left(y+7\right)}\)
\(=\frac{\left(y-2\right)\left(y+7\right)}{\left(y+3\right)\left(y-3\right)\left(y+7\right)}-\frac{\left(y-7\right)\left(y+3\right)}{\left(y-3\right)\left(y+7\right)\left(y+3\right)}\)
\(=\frac{\left(y-2\right)\left(y+7\right)-\left(y-7\right)\left(y+3\right)}{\left(y+3\right)\left(y-3\right)\left(y+7\right)}\)
\(=\frac{9y+7}{\left(y+3\right)\left(y-3\right)\left(y+7\right)}\)