Prudence, a mean business law teacher, offers $50 to any student who will mow her lawn. Sam goes right over and begins mowing. Just before he finishes, Prudence goes over and tells him that she revokes her offer. Which of the following is true regarding Sam's entitlement to payment?
Sam is entitled to recover because a unilateral contract was involved, and he was entitled to a reasonable amount of time in which to complete the job.