How do I factor the following? Thanks.

1. ax+bx+ay+by
2. 3x^2-6xy+2x-4y
3. 6+2y+3x^2+x^2y
4. 6x^2+7x+2
5. 4x^2-9x+3
6. 5y^2+13y+6
7. 6x^2+19x+3
8. 16x^2+16x+3