An absolute value is the positive value of the number between the vertical lines.
If the number in between the vertical lines is negative, the absolute value become a positive.
If the value in between the lines is already positive, it stays positive.
17. |-8| = 8
18. |13| = 13
19. |3 6/7| = 3 6/7
20. |-1.34| = 1.34