3 * (х+12,6) - х = 26,18

3 * (х + 12,6) - х = 26,18;

3 * х + 12,6 * 3 - х = 26,18;

3 х + 37,8 - х = 26,18;

2 х + 37,8 = 26,18;

2 х = 26,18 - 37,8;

2 х = - 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.