Correction :

12 - 4 = 87 + 12 = 19
19 - 17 = 28 + 5 = 13
43 - 19 = 2411 - 9 = 2
5 + 11 = 1638 - 14 = 24
20 + 5 = 2528 : 7 = 4
20 - 3 = 1711 × 5 = 55
12 + 10 = 2224 + 24 = 48
33 - 12 = 217 + 10 = 17
18 - 4 = 142 + 22 = 24
11 + 11 = 2228 - 19 = 9