Correction :

7 + 2 = 9	5 + 15 = 20
9 + 13 = 22	12 + 7 = 19
5 + 18 = 23	14 + 10 = 24
20 + 6 = 26	9 + 4 = 13
8 + 12 = 20	7 + 7 = 14
28 - 24 = 4	26 - 24 = 2
22 - 9 = 13	15 - 11 = 4
3 + 14 = 17	10 + 17 = 27
2 : 2 = 1	8 + 11 = 19
19 + 20 = 39	6 × 6 = 36