Correction :

4 × 7 = 28	18 - 5 = 13
15 - 5 = 10	9 × 1 = 9
27 - 23 = 4	11 × 8 = 88
28 - 10 = 18	15 + 5 = 20
19 + 12 = 31	6 × 7 = 42
2 + 18 = 20	42 : 6 = 7
7 + 22 = 29	10 + 16 = 26
18 - 4 = 14	2 + 16 = 18
24 + 0 = 24	17 + 1 = 18
24 + 6 = 30	45 - 24 = 21