There are four elements to a contract: agreement, capacity, consideration, and legality. To determine if a contract exists, a court would have to decide that an agreement between Cassie and Kevin exist. Then the court would have to determine what consideration exists. Mowing the yard consideration. Third, the court would have to determine if both parties have capacity to contract. Both parties appear to be mentally fit, not intoxicated, and the minimum age. Finally, the court would have to decide if a contract for yard work legal. Kevin expressly agree to the contract. His behavior at the window likely permission for Cassie to mow. Because the parties have a history of agreements for lawn mowing, there likely an implied in fact contract. In this case, Cassie service. Kevin provide a service to Kevin. Cassie know that she expected to be compensated. Because of the size of the yard, it be fair for Kevin not to pay Cassie. Under these facts, there an express contract. There an implied in fact contract. There select answer an implied in law contract