Seller agreed to deliver gasoline to Buyer at $3.15 per gallon over a period of one year. By the sixth month, gasoline had increased in price over a dollar a gallon. Although Seller had gasoline available for sale, he told Buyer the price would have to increase by that much or he would be unable to deliver. Buyer agreed to the increase, but when billed, refused to pay the additional amount. Is Buyer bound by hispromise to pay the increase? Explain.