Answer:
The answer is: Joan is not bound to buy Jack's car.
Explanation:
Jack is the offeror in this sales offer (the person that offers to sell a product) and Joan is the offerre (the person that wants to buy the product). In order for any agreement to be bounding, both the offeror and the offerre must accept the agreement's conditions. There are multiple reasons why Joan may have not been able to even look at Jack's offer, and unless she accepts it, it has no legal value.
As an extreme example, I can not send Tim Cook an offer to buy Apple Corporation for $10 and give him 10 days to reject the offer or else I would immediately become the owner of Apple Corporation.
