Correction :

6 + 19 = 25	16 + 23 = 39
26 - 21 = 5	14 + 13 = 27
3 + 6 = 9	8 + 19 = 27
12 + 6 = 18	24 + 4 = 28
18 - 6 = 12	18 + 21 = 39
31 - 18 = 13	12 - 12 = 0
7 + 4 = 11	24 + 5 = 29
11 × 3 = 33	30 - 15 = 15
80 : 10 = 8	13 - 7 = 6
6 : 1 = 6	28 - 8 = 20