Anyone please help me answer this

Case Problem 2: Rex Publishing sold 100 books to a certain Professor X who ordered these by telephone, which was agreed to be payable on delivery. The books were subsequently delivered to him with the corresponding invoice, and he paid with a personal check. Professor X then sold the 50 of the books to Jean Gray who asked for verication, and was then showed the invoice for the books. Rex Bookstore became suspicious when Professor X ordered another set of books even before his check cleared. Upon investigation, Rex found that he wasn't the person he claimed to be (Dean in St. Louis University). Rex further suspected when the check paid by Professor X was dishonored by the bank. Rex had the police capture Professor X, as well as seize the books from Jean Gray who in turn demanded the return of the books. Question: Whether or not there is a perfected contract of sale between Professor X and Rex Bookstore. Explain your answer (10 points)