4. 9-6, 9-5, 9-4, 8+7, 7+7, 7+6, 2+6-4, 3+5-6, 6+3-8, 18-8-10, 19-10-9, 17-17+8

9 - 6 = 3

9 - 5 = 4

9 - 4 = 5

8 + 7 = 15

7 + 7 = 14

7 + 6 = 13

2 + 6 - 4 = 4

3 + 5 - 6 = 2

6 + 3 - 8 = 1

18 - 8 - 10 = 0

19 - 10 - 9 = 0

17 - 17 + 8 = 8