Daisy is Pen's sister. Daisy loans Pen $4000 that Pen uses to purchase a car. Before Daisy paid the money to Pen, she had Pen sign a written agreement in which Pen agreed to pay back the $4000 on 15 March 2019 plus an additional $400 for interest and the inconvenience to Daisy of not having the $4000 available to her for a whole year. Is this a legally enforceable contract?