Ok, so from I) we know that x<y, thus clearly not sufficient. II) we know that z<0, so the denominator is negative, and for the statement to be true, the numerator (x+y) must be negative as well. But, we can't determine if x is pos or neg. II) alone is not sufficient.

Both statements put together, z must be negative, x<y, and x+y<0 to satisfy the statement. I think the answer is yes, X<0 and it takes both statements together to be sufficient. If you let x be a postiive number, y must be a greater positive number and thus does not follow that x+y<0.

for x+y/z>0 -
1. (x+y) and z are both positive
2. (x+y) and z are both negative

using A - Insufficient
using B - Insufficient

If you combine the two -
x<y - means (x+y) is negative and z is negative - sufficient.