If I understand what you are asking, then the | | symbols are absolute value symbols. That means that if a number is negative within those lines, then that number is no longer negative. However, if a positive number is within those lines, then the number stays the same.
If you have a problem like |-12| - |3|, then simply do 12 - 3, or 9. However, you would write it as |9|. Hope this helps!
