Ответ:

6

Пошаговое объяснение:

1) 3. 1/7 * (-4) = 22/7 * (-4) = -88/7 = -12. 4/7

2) 1,8 : (-0,1) = -18

3) 20/21 : 1. 2/3 = 20/21 : 5/3 = 20/21 * 3/5 = 4/7 * 1/1 = 4/7

4) -12. 4/7 - (-18) + 4/7 = -12. 4/7 + 18 + 4/7 = -12. 4/7 + 17. 7/7 + 4/7 = 5. 3/7 + 4/7 = 5. 7/7 = 6