Concept: The question tests on the basics of Absolute values



=>b=7   or

- (2b-6)= 8

=> b=-1    (Using the fundamental concept of Absolute values

=> |x-a| = x-a if x>=a   &   (a-x )if x < a

According to the question, you can also say that |2b-6| = 8 implies that   the distance between b and 3 is equal to 4 implying that b could be -1 or 7.