The absolute value of a number is the distance from 0 to that number. The distance is positive, hence, the absolute value is always a positive number.
Replace the value of x:
[tex]| x - 8 |[/tex]
[tex]| -4 - 8 |[/tex]
[tex]| -12 | = \large{\boxed{12}}[/tex]
The absolute value of a number is the numerical value of the number, without regard to its sign.