Ответ:

Пошаговое объяснение:

1)

-1/4 + 3/5 = -5/20 + 12/20 = 7/20

2)

9/11 + (-2/5) = 9/11 - 2/5 = 45/55 - 22/55 = 23/55

3)

-20/21 + 3/7 = -20/21 + 9/21 = -11/21

4)

7. 5/12 + (-3. 7/24) = 7. 5/12 - 3. 7/24 = 7. 10/24 - 3. 7/24 = 4. 3/24 = 4. 1/8

5)

-6. 11/12 + (-8. 13/18) = -6. 11/12 - 8. 13/18 = -6. 66/72 - 8. 52/72 = -14. 118/72 = -15. 46/72 = -15. 23/36

6)

-5. 12/35 + 10 = -5. 12/35 + 9. 35/35 = 4. 23/35