1.
5х + 11 = 7х + 31
5х - 7х = 31 - 11
-2х = 20
х = -10
2.
(12х + 11) - 8 = 13х - 7
12х + 11 - 8 = 13х - 7
12х - 13х = -7 - 11 + 8
-х = -10
х = 10
3.
10(8х - 3) = 140 + 7(3х + 1)
80х - 30 = 140 + 21х + 7
80х - 21х = 140 + 7 + 30
59х = 177
х = 3
4.
48 = 11 - (9х + 2)
48 = 11 - 9х - 2
48 = 9 - 9х
9х = 9 - 48
9х = - 39
х = 