Correction :

16 - 4 = 12	35 - 23 = 12
15 - 1 = 14	40 : 5 = 8
12 - 1 = 11	21 + 19 = 40
11 - 5 = 6	9 × 11 = 99
34 - 12 = 22	35 : 7 = 5
19 - 1 = 18	6 : 6 = 1
8 : 1 = 8	31 - 12 = 19
15 - 12 = 3	5 + 11 = 16
42 : 7 = 6	5 + 23 = 28
14 - 14 = 0	20 + 1 = 21