Answer:
b.Sally wins; there was never any offer for Mary to accept.
Explanation:
When Sally says that she thinks the coat is worth about $5,000 that was just a valuation in response to Mary's inquiry, and that doesn't constitute a valid legal-binding offer in any way. In fact, Sally explicitly says she is not sure she even wants to sell the coat. In order for an offer to be recognized there must be a clear intent to engage in a contract from both parties and that isn't the case since Sally never specified an asking price nor did Mary make a concrete offer at the moment. Therefore, Sally wins; there was never any offer for Mary to accept.