Условие:

40 + 28 + 2
20 + 56 + 4
70 − (12 + 4)
100 − (28 − 2)

40 + 28 + 2 = 40 + (28 + 2) = 40 + 30 = 70
20 + 56 + 4 = 20 + (56 + 4) = 20 + 60 = 80
70 − (12 + 4) = 70 − 16 = 70 − (10 + 6) = 70 − 10 − 6 = 60 − 6 = 54
100 − (28 − 2) = 100 − 26 = 100 − (20 + 6) = 100 − 20 − 6 = 80 − 6 = 74