Frank writes to Ben on 1 July offering to sell him his sailing boat for 1200. On 8 July,having a received no reply, he decides to withdraw this offer and sends a second letter. On 10 July,Ben receives the original offer letter and immediately telephones his acceptance to Frank's wife. He follows this up with a letter posted the same day. Frank's second letter arrives on 14 july and Ben learns that Mel has bought the boat the previous day. What is the legal situaion?