Evaluate |x-13| when x=5.
a.8
b.-8
c.21
d.-21

5 - 13 = -8

But remember it is in the ||. This means the answer will, no matter what, be positive.

So the answer is |-8|, or +8.

A is the answer.

Now for an explanation of why the || makes it positive.

They are know as "absolute values." Absolute values will always, no matter what, be a positive number. These can be very tricky to deal with, but just remember to answer what is in the || first, and THEN do the absolute value. Remember that on a number line, the middle is always 0. And because -8 and 8 are both 8 spaces away from 0, the absolute value will be 8. This is why it is positive. You cannot be negative spaces away from something.