Correction :

31 - 20 = 11	12 + 24 = 36
4 + 1 = 5	10 - 3 = 7
14 + 6 = 20	3 + 13 = 16
21 + 0 = 21	33 - 24 = 9
14 + 16 = 30	14 - 1 = 13
17 + 6 = 23	28 - 8 = 20
12 + 13 = 25	21 - 3 = 18
9 + 16 = 25	14 - 0 = 14
18 + 5 = 23	40 - 21 = 19
19 - 18 = 1	9 × 6 = 54