Walker Trucks and Pat Garret are experienced farmers. Walker Trucks recently agreed to sell to Pat Garret a cow for only $80 because both parties believed the cow was sterile. When Walker discovered that the cow was pregnant and, therefore, worth at least $1,000, he refused to deliver. However, Pat Garret wants that cow and is getting ready to sue Walker. Is Walker obligated to deliver the cow? Who is likely to win at trial? B) Rastafa offers to sell a piano for $1,000, without knowing that it is actually worth $2,500. Marta accepts, believing it to be worth $1,500. After they formed a contract, but before the piano was delivered, Elton John (recognized expert on piano value) came to Rastafa's house and told him that the piano was worth $2,500. Now Rastafa does not want to deliver the piano although he has a valid contract with Marta. Naturally, Marta plans to bring a lawsuit to enforce the contract. Is Rastafa obligated to deliver the piano? Who is likely to win at trial?