Sam puts an ad in the newspaper stating that she wants to sell her alpaca for $500. Angela goes to Sam's home and tells her that she is interested in buying the alpaca. After petting it and inspecting its feet, Angela hands Sam $500 in cash, which Sam puts in her pocket. Just then, Steve drives up and tells Sam that he'll give her $600 for the alpaca. Sam hands Angela back her $500 and sells the alpaca to Steve. Because she needs the alpaca for her sweater business, Angela sues Sam for breach of contract.

 

Is there a valid contract? Why or why not?