Условие:

63 + 7
34 + 6
42 + 8
15 + 50

63 + 7 = (60 + 3) + 7 = 60 + (3 + 7) = 60 + 10 = 70
34 + 6 = (30 + 4) + 6 = 30 + (4 + 6) = 30 + 10 = 40
42 + 8 = (40 + 2) + 8 = 40 + (2 + 8) = 40 + 10 = 50
15 + 50 = (10 + 5) + 50 = 5 + (10 + 50) = 5 + 60 = 65