Marilyn Stein's mail carrier delivers a book with a letter enclosed. The letter states that the book is on sale for half its normal price and, if she doesn't want it, she must return it by a certain date or be billed for it.

a) Does Stein have any obligation, either by common law or statute to pay for this book?

b) Do her rights change if she starts to read the book, and then decides she doesn't want it?