Find the slope of the line through each pair of points.
1) (-13, 15).(-7, 12)
2) (-8, -8), (0.-20)
3) (-3, 3), (-11, -11)
4) (-11, 8), (-8, 3)
5) (16, 19), (-14, -18)
6) (-17,-10), (3, 17)