Answer:
a. No, because Shelby made a mistake about the dog's value, not a mistake about a material fact.
Step-by-step explanation:
Peggy made an offer to sell the dog for $800, they didn't discuss the dog's ancestry and Shelby wrongly assumed the dog was from champion lines and agreed to buy the dog for $800.
Based on further investigations, she discovered the dog was worth just $200.
She cannot rescind the contract because she wrongly assumed the dog's value not an error about à material fact. Peggy sold the dog at her own rates and Shelby bought the dog while wrongly assuming the value, so she cannot cancel the contract based on that.