8+(-2 5/7) = 8 - 2 5/7 = 8 - (2 + 5/7) = 8 - 2 - 5/7 = 6 2/7

-4 2/5+3,4 = -4 2/5 + 3 4/10 = -4 2/5 + 3 2/5 = -1 4/5

-6,5+3 1/2 = -6 1/2 + 3 1/2 = -3

7 2/3+(-9) = 7 2/3 - 9 = 6 5/3 - 9 = 6 - 2 1/3 = 3 2/3