Discuss the contractual rights of Anita, Dan and Cathy?

I’m working on a business law writing question and need an explanation and answer to help me learn.

On November 1, Anita sent a letter to Dan with whom she had been negotiating a contract to sell all of
her law textbooks for HK$10,000. The letter said that unless Dan could reply by returning mail on
or before November 7, the offer would lapse. Unfortunately, Anita’s letter contained an error in the
address and was not delivered to Dan until November 6 at 9 a.m. Dan replied immediately accepting
the offer and posted a letter on November 6 at 12 noon.

On November 4, Cathy, knew about the negotiation, sent message via WhatsApp (i.e.: a popular
online chat platform) to Anita to express the interest to buy her textbooks for HK$8,000. Anita
having heard nothing from Dan then, telephoned Cathy on November 5 and offered the purchase price
at HK$9,000. Cathy accepted.

Anita sent an email to Dan’s wife (Linda) on November 6 telling her that the offer of November 1 was
withdrawn. This email was received on Linda’s computer at 11:00 a.m. on November 6, but was not
opened and read by Linda until the next day.

State the legal principles applicable to each issue, including relevant case law and legislation.

Analyse the facts and make assumptions if necessary.

You may argue against certain established law and principles as long as sufficient reasoning is
given to support your point of view.