Brad sends a letter to Carol on September 1st offering to sell his car to her for $2500. Carol receives the letter on September 5th, and mails back an unconditional acceptance the same day. Brad receives the letter on September 10th. In the meantime, Rachel approaches Brad on September 7th, and offers him $3000 for the car. He accepts. Do all the elements of a contract exist in this scenario? If so, has Brad breached his contract with Carol?