Correction :

30 - 15 = 15	16 + 5 = 21
20 - 15 = 5	17 - 14 = 3
5 - 2 = 3	11 + 12 = 23
81 : 9 = 9	0 + 11 = 11
24 - 12 = 12	45 - 24 = 21
9 × 11 = 99	8 + 5 = 13
37 - 23 = 14	18 - 16 = 2
1 + 4 = 5	13 - 4 = 9
16 - 12 = 4	18 - 12 = 6
12 - 0 = 12	1 × 4 = 4