6. 7 + 7 - 5, 4 + 9 - 3, 48 - 40 + 6, 56 - 50 + 7, 34 - 4 - 30, 87 - 7 - 80

7 + 7 - 5 = 14 - 5 = 9

4 + 9 - 3 = 13 - 3 = 10

48 - 40 + 6 = 8 + 6 = 14

56 - 50 + 7 = 6 + 7 = 13

34 - 4 - 30 = 30 - 30 = 0

87 - 7 - 80 = 80 - 80 = 0