David was unemployed and suffered from a number of disabilities. To try to get him back into the workforce, Sam arranged for David to paint his (Sam's) house. The arrangement was initially to be on a trial basis in order to determine whether David was capable of doing the job. Under the arrangement, Sam agreed to pay David $25 per hour as a starting rate; if he proved that he could complete the task, they would then discuss the rate of payment again.Discuss if there is a valid contract between david and sam.