Peter authorized Arnon, a grain broker, to buy at the market 20,000 bushels of wheat for Peter. At the time, Arnon had in storage 5,000 bushels belonging to Johnson, who had authorized Arnon to sell for him. Arnon also had 15,000 bushels that she owned. Arnon transferred these 20,000 bushels to Peter's name and charged Peter the current market price. Shortly thereafter, and before Peter had used or sold the wheat, the market price declined sharply. Peter refused to pay for the wheat and tried to cancel the contract. Can he cancel? Explain.