\frac{3cos\alpha-2sin\alpha}{sin\alpha-5cos\alpha}=\frac{cos\alpha(3-2\frac{sin\alpha}{cos\alpha})}{cos\alpha(\frac{sin\alpha}{cos\alpha}-5)}=\frac{3-2tg\alpha}{tg\alpha-5}=
=\frac{3-2*\frac{2}{5}}{\frac{2}{5}-5}=\frac{3-\frac{4}{5}}{\frac{2-25}{5}}=\frac{\frac{15-4}{5}}{\frac{-23}{5}}=\frac{\frac{11}{5}}{-\frac{23}{5}}=-\frac{11}{5}*\frac{5}{23}=-\frac{11}{23}