21 - 7 = 14, 14 - 7 = 7, 7 - 7 = 0, 21 : 7 = 3
45 - 15 = 30, 30 - 15 = 15, 15 - 15 = 0, 45 : 15 = 3
36 - 9 = 27, 27 - 9 = 18, 18 - 9 = 9, 9 - 9 = 0, 36 : 9 = 4
50 - 10 = 40, 40 - 10 = 30, 30 - 10 = 20, 20 - 10 = 10, 10 - 10 = 0, 50:10=5
70 - 14 = 56, 56 - 14 = 42, 42 - 14 = 28, 28 - 14 = 14, 14 - 14 = 0, 70:14=5