Vince offers to buy a book owned by Sun-Hi for twice what Sun-Hi paid for it. She accepts and hands the book to Vince. Sun-Hi's delivery of the book is

Vince and Sun-Hi's Book

With Sun-Hi's delivery of the book, the offer by Vince is accepted by Sun-Hi.

Acceptance of an offer is necessary to make a contract.

Explanation:

An offer by Vince is not a contract, but its acceptance by Sun-Hi without a counter-offer makes it a valid contract that can be enforced in law if other ingredients for a valid contract are present.  Acceptance establishes the agreement between Vince and Sun-Hi.  Once Sun-Hi accepts Vince's offer with valid considerations (the book and double the price), the agreement for a business transaction between them is consummated.  It is acceptance that completes the exchange of promises in this simple contract.

answer; institution based;

answer; the cpi;