Please help me in solving this behavioral economics question ASAP. Thanks.

2. Prove the following statement: Given a utility function u( ) representing a rational preference relation >, x * y # u(x) = u(y) (Hint: Your proof should have two separate parts: one where you prove x * y implies u(x) = u(y), and a second where you prove u(x) = u(y) implies x ~ y)