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.