Concept: The question tests on the application of using equations to reach at a conclusion in a DS format

Solution:

We are asked if a-1/b+1  =  a/ b

Or we are asked if b (a-1) = a(b+1)   [On cross multiplying]

Or if b a –b = a b + a 

= > If   a =  -b   ?

 

St (1)  a= b-4

If b= 2 then a= 2-4 = -2 and hence a is EQUAL to –b (Yes)

However if b =4 a=0   and a is NOT EQUAL to –b (No )

Hence, two contradictory answers and thus St (1) is Insufficient

 

St (2) a = -b 

It’s exactly what we are asking for in the question stem.

Thus sufficient.  Option (B)