On Friday 10 December the following advertisement is placed in the window of Ann's art gallery: '2 copies of a very rare Blake print-$15,000 each, acceptance to be made face-to-face'. Chas and Dave are very keen to acquire the prints but think that the price is too high. They each offer Ann $12,000 for a copy but she refuses to sell the prints at that price, although she says she will accept $13,500. Moreover she promises she will keep her offer to them open until 12o'clock on the following Monday, 13 December. On the Sunday before the deadline Chas and Dave have to leave the country on business but before they do so each post a letter stating that he agrees to buy one of the prints at the price of $13,500. Both letters arrive on the morning of Tuesday 14 December. In any event Ann had already sold both prints to Eve on Saturday 11 December for a total price of $30,000.

Analyse the above situation from the point of contract law. In particular advise the parties as to their rights and liabilities under contract law