а)
29/36 + 5/54 = 29/36 + 10/108 = 29/36 + 5/36 = 34/36 = 17/18

б)
0,36 - 9/75 + 2/15 = 36/100 - 9/75 + 2/15 = 36/100 - 36/300 + 60/300 = (36 - 36 + 60) / 300 = 60/300 = 1/5

в)
(1/2 - 1/3) - (1/4 - 1/5) = 3/6 - 2/6 - 1/4 + 1/5 = 1/6 - 1/4 + 1/5 = 10/60 - 15/60 + 12/60 = (10 - 15 + 12) / 60 = 7/60

2)

а)
3/4 - (x + 1/20) = 1/5
3/4 - x - 1/20 = 1/5
15/20 - 1/20 - x = 1/5
14/20 - x = 4/20
-x = -10/20
x = 1/2

б)
2/3 - (x - 1/21) = 2/7
2/3 - x + 1/21 = 2/7
14/21 - 21x + 1 = 6/21
15/21 - 21x = 6/21
-21x = -9/21
x = 3/7