Can someone look at this problem? This is from GMATClub Challengeshttp://gmatclub.com/tests/m/02/#q25
Also, is it possible for the variable y to have two different values for 2 cases?
yes it is possible that you may end up with different values for 2 cases.
In this case it should be D.
1) y = x + y = 3
2) y = x + y => x - y + y = 0 => y = -2