Solve the math problem.
4 - 2 =
8
- 7
11
- 6
8 - 8 =
17 - 2 =
14
- 0
19
12 - 5 =
15
- 1
6 - 6 =
9
- 9
- 2
7 - 5 =
16
- 5
17 - 4 =
8 - 2 =
18
18 - 9 =
17 - 6 =
20
12 - 3 =
13 - 7 =