Answer:
-y+z
Step-by-step explanation:
You didn't list a full equation. Is this is as far as you can simplify this with the info given. to get it to that point just subtract 2y from y. If you meant Y=z-2y then the answer would be 3y=z or Y=z/3 (the same things just more is more simplified). For a more complete answer gove more information.