Here, 'B' stands for 'bracket' ,'O'for 'of' , 'D' for' division' and 'M' for 'multiplication', 'A' for 'addition' and 'S' for 'subtraction'.
Thus, in simplifying an expression, first of all the brackets must be removed, strictly in the order(), {} and [].
After removing the brackets, we must use the following operations strictly in the order:
|a| ={a, if a>0
-a, if a < 0
Thus, |7|=7 and |-7|=-(-7)=7.