After 40 years working on the plant floor at Manufacturing Company, Darby decides it is time to retire. He sends an e-mail to the Company President informing him that this will be his last month on the job and that he's retiring at the end of the month. Company President calls Darby into his office and tells him, "Darby, you've been an exemplary employee for such a long time. We hate to see you go, but want you to know that , while the Company doesn't have a retirement plan, the Company will pay you a weekly paycheck of $500 for the rest of your life. It's our way of saying thank you " Is Company President's promise to pay $500 a week enforceable under the theory of promissory estoppel