You are given a question and two statements. Identify which of the statements is/are sufficient/necessary to answer the question.
Which is the heaviest of the four objects X, Y, Z and M?
Statements:
I. X and Z together weigh as much as Y and M together. X is twice as heavy as M and half as heavy as Z.
II. X is twice as heavy as M and half as heavy as Y, while Z is one and a half times as heavy as X.