Ответ:

Пошаговое объяснение:

5/7 + 1/7= 6/7

5/7 - 1/7= 4/7

3/9 + 2/9= 5/9

3/9 - 2/9= 1/9

6/11 + 2/11= 8/11

6/11 - 2/11= 4/11

5/13 + 3/13=8/13

5/13 - 3/13= 2/13

15/17 + 1/17= 16/17

15/17 - 1/17= 14/17

11/19 + 6/19= 17/19

11/19 - 6/19= 5/19

8/15 + 2/15= 10/15= 2/3

8/15 - 2/15= 6/15= 2/5

8/21 + 2/21= 10/21

8/21 - 2/21= 6/21