Betty prepared a letter offering to sell Barney her car for $10,000, with the cash payment and delivery to take place on March 31. Betty brought the letter to the post office and mailed the letter to Barney on March 1. Barney received the letter on March 4. The last paragraph of the letter stipulated that Betty must receive Barney's acceptance no later than 5 p.m. on March 13. On March 10, Barney mailed a letter to Betty accepting Betty's offer to sell the car. The letter was not received by Betty until March 15. On March 13 at 6:00 p.m., Betty called Barney and told him that she was revoking her offer. On the same day, Betty sold her car to Dino. Barney sued Betty for breach of contract. What is the basis for Barney's lawsuit, and what are Betty's best arguments to defend against Barney's claim?