Charles contracts to supply Peter with 10,000 lbs of wheat per month for 24 months, for a fixed sum of $US20,000, payable in advance. After six months the market price of wheat unexpectedly doubles, due to the outbreak of war in Ukraine (the main wheat-producing country). Peter, hearing that as a result of this Charles has started to cancel similar contracts, suggests to Charles that he will be prepared to take 7,000 lbs of wheat per month in satisfaction of their contract. Charles agrees, and delivers 7,000 lbs of wheat per month for the next five months. The war in Ukraine then ends and the market price of wheat collapses. Peter now demands: (a) the 15,000 lbs shortfall in deliveries in relation to the past five months; and (b) 10,000 lbs of wheat per month for the rest of the contract. Advise Charles.