Arnold is a pesticide specialist who runs his own business and, as such, obtains most of his work on a contract basis. Arnold agrees to spray the inside of Napoleon's house, except the kitchen and bathroom. It is a term of the contract that the relevant rooms will be sprayed twice for a total fee of $15,000. Arnold sprays the house once and finds that he miscalculated the quality of the pesticide he was using. It would be a waste of pesticide and labour to spray the house again as it would not improve the quality of the job nor would it lengthen the period of protection provided by the pesticide. Arnold approaches Napoleon and explains that a second spray would not add anything to the quality of the work. Napoleon says "OK, I'll take your word for it. Why don't you give the kitchen and bathroom a spray and we'll call it even?' Arnold agrees, on the condition that he can have a full week's break as his back is sore. (Napoleon has a large house and Arnold's business relies solely on his own labour.) Napoleon agrees. Two days later Napoleon calls Arnold as he has changed his mind, saying 'Mate, I know what we said but we are sick of this smell. We want the kitchen and bathroom done and we want it done now. Either finish the job or you won't get paid. Arnold seeks your advice as to whether he has to comply with Napoleon's demands