OMG thank you so much! I completely misread the question thinking that it said that Y is not negative.

ady871 wrote:

Hi !

I do not quite understand why statement B is not sufficient- since they tell us at the beginning that Y is not zero therefore Y must be equal to 4 and hence makes this statement sufficient?

The question asks whether y is positive. From (2) we have TWO values of y, one positive, 3, and one negative, -4. So, we cannot answer the question, whether y is positive, which means that this statement is NOT sufficient.