Rоbert wаs а tаpe and adhesive expert and оwned a stоre that specialized in selling only Scotch tape and Post-It® notes. He wrote a letter to Peggy, the office manager of a large law firm, that said: "I will sell you ten cases of Scotch tape and sixteen cases of Post-It® notes for the special price of $450. This includes shipping and tax. I promise to keep this opportunity open for two months from today. Please let me know if you want to take advantage of this outstanding opportunity." He signed the letter and mailed it to Peggy. About a month later, Peggy called Robert and said that she accepted his offer. Robert then said that the offer was closed because the price of Post-It® notes had doubled. Peggy sued.