1) (12/31 + x) – 7/31 = 19/31
12/31 + x = 19/31 + 7/31
12/31 + x = 26/31
x = 26/31 – 12/31
x = 14/31
2) 18/43 – (x – 14/43) = 9/43
x – 14/43 = 18/43 – 9/43
x – 14/43 = 9/43
x = 9/43 + 14/43
х = 23/43
3) 34/37 – (x + 12/37) = 22/37
x + 12/37 = 34/37 – 22/37
x + 12/37 = 12/37
x = 12/37 – 12/37
х = 0
4) (x + 12/37) + 4/37 = 17/37
x + 12/37 = 17/37 – 4/37
x + 12/37 = 13/37
x = 13/37 – 12/37
х = 1/37
5) (x – 5/29) + 4/29 = 4/29
x – 5/29 = 4/29 – 4/29
x – 5/29 = 0
x = 0 + 5/29
x = 5/29
6) 15/59 + (27/59 – x) = 17/59
27/59 – x = 17/59 – 15/59
27/59 – x = 2/59
х = 27/59 – 2/59
x = 25/59