Question

find the absolute value -15

Answer 1

recall the definition of |x|:

|x| = x if x >= 0
|x| = -x if x < 0

so, since -15 < 0, |-15| = -(-15) = ?

Answer 2

The distance of a number from the origin of a number line is called the absolute value of the number. The absolute value of +20 is the same as the absolute value of -20, because they are the same distance from the origin:
|20| = 20, and |-20| = 20.