Ellie owns a 1968 Ford Mustang and, in order to raise a deposit for her new house, she decided to sell the vehicle to Sam, a mechanic, for $30,000. As part of the deal, Ellie agreed to have it restored for Sam. Ellie asked Richard, a vintage car restorer, to carry out the work within eight weeks for $3,000. A month later, Ellie was worried that Richard would not meet the deadline and, eventually offered him an extra $1,000 if the restoration was completed on time. Sam was anxious to have the car on time as he was going to sell it on and had a purchaser for it, so he offered to give Richard $500 for doing the work. Richard completed the restoration on time but Ellie has refused to pay him the extra $1,000, arguing that Richard was already obliged to complete the work for $3,000. Furthermore, Sam has told Richard that he can only give him $100, which Richard has reluctantly agreed to accept.