3*(х+12,6) – х = 26,18

3 * (х + 12,6) – х = 26,18;

3 * х + 12,6 * 3 - х = 26,18;

3х + 37,8 - х = 26,18;

2х + 37,8 = 26,18;

2х = 26,18 - 37,8;

2х = - 11,62;

х = - 11,62 : 2;

х = - 5,81;

3 * (- 5,81 + 12,6) – (- 5,81) = 26,18;

3 * 6,79 + 5,81 = 26,18;

20,37 + 5,81 = 26,18;

26,18 = 26,18.