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