Find the slope of the line through each pair of points.
6) (-2,-1), (-1,0)
7) (-7,-4), (-13,-13)
8) (-14,-14), (-11,-9)
9) (17,-13), (-7,-13)
10) (7,4), (15,-18)
11) (4,14), (-2,17)
12) (-18,-10), (-18,15)
13) (13,-15), (14,-3)
14) (5,5), (-11,-6)
15) (3, -19), (-7,11)