Bob writes to Tom, a known collector of comics, asking if he wants to buy his rare 1999 edition of a Superman comic for 1000.He posts the letter by 1^st class on 20th August.Tom receives the letter on 25^th August and writes back to Bob, agreeing to pay 1000 for the comic, posting his response on 27^th August by second class post.

On 30^th August,Bob changes his mind about selling the comic toTom because Rex has offered him 1100 for the comic. He emailsTom on 31^st August, saying that he no longer wishes to sell the comic to him.Tom is very angry and threatens to sue Bob.

John , 17, offersto sell his toy car collection toBob for 120,Bob accepts. All communication is evidenced by email. The next dayJohn says he will not fulfil the contract as he has changed his mind.

With reference to case law, adviseBob on his legal position in respect ofTom and John.