здравствуй.

a) 1 - 7/9 = 9/9 - 7/9 = 2/9

-1 + 7/9 = -9/9 + 7/9 = -2/9

-1 - 7/9 = -1 7/9

b) -3.4 - 8 = -11.4

3.4 - 8 = -4.6

-3.4 + 8 = 4.6

удачи в учебе.