Correction :

15 + 2 = 17	20 - 10 = 10
6 : 1 = 6	5 - 2 = 3
4 + 9 = 13	18 - 14 = 4
2 + 5 = 7	18 - 9 = 9
35 - 14 = 21	15 - 2 = 13
21 - 4 = 17	20 + 22 = 42
23 - 23 = 0	11 - 8 = 3
24 + 21 = 45	19 + 19 = 38
28 - 7 = 21	2 + 16 = 18
22 - 8 = 14	11 - 5 = 6