Пошаговое объяснение:

№3

а) 4/7 + 2/9 = 36/63 + 14/63 = 50/63

б) 11/15 - 11/18 = 66/90 - 55/90 = 11/90

№4

а)

15 2/15 - х = 4 4/3

х = 15 2/15 - 4 4/3

х = 15 2/15 - 4 20/15

х = 15 2/15 - 5 5/15

х = 14 17/15 - 5 5/15

х = 9 12/15

х = 9 4/5

б)

(5/6 - х) + 2/3 = 13/18

5/6 - х = 13/18 - 2/3

5/6 - х = 13/18 - 12/18

5/6 - х = 1/18

х = 5/6 - 1/18

х = 15/18 - 1/18

х = 14/18

х = 7/9

№5

1) 13 5/12 + 2 11/18 = 13 15/36 + 2 22/36 = 15 37/36 = 16 1/36

2) 25 - 8 3/4 = 24 4/4 - 8 3/4 = 16 1/4

3) 16 1/4 + 16 1/36 = 16 9/36 + 16 1/36 = 32 10/36 = 32 5/18