I hope this helps
We have to prove that Is z < 0?
Statement 1. xy>0 and yz<0
=> x & y are negative / x & y are positive
=> z is postive / z is negative
Insufficient since nothing said about y or z
X is positive
= >X is positive Y is positive Thus Z is negative
Giving +1 kudos is a better way of saying 'Thank You'.