Justin's auntie tells Justine, "Justine, you are spending too much time going out when your HSC exams are near. I will reward you $2,000 if you stop going to parties, drinking and get an ATAR of 97.95". Justin decides that $2,000 is a good incentive and stopped partying, drinking and, after working very hard, he obtained an ATAR of 98. When Justin goes to his auntie for his reward, Justine's auntie replies, "Good job, Justine, but surely you know I was just joking; besides this success is beneficial to you." Can Justine enforce the $2000 reward from his auntie?Why or why not?