Sharri places an advertisement in the paper offering to sell her piano for $4,000. Aaron writes to Sharri in response to the advertisement and offers to buy her piano for $3,000. Sharri receives Aaron's offer on January 3 and telephones him to ask whether he will consider increasing his offer. Aaron tells her he will think about it. Mary writes to Sharri, offering to buy her piano for $3,200. Sharri receives the letter on January 5. She writes to Mary the same day and tells her she will sell the piano for $3,500. Mary receives the letter on January 7, and writes back the same day advising Sharri that she accepts the offer to buy the piano for $3,500. Unfortunately, the letter is lost in the mail, and Sharri never receives it. Aaron writes to Sharri on January 5 stating that he will pay her $4,000 for her piano by paying her $3,000 now and $1,000 in one month. Sharri receives Aaron's letter on January 8 and telephones Aaron the same day to confirm that the payment terms are acceptable. Sharri then receives a telephone call from Mary on January 9 in which she learns of Mary's acceptance by letter dated January 7. Sharri then tells Mary she now wants $4,000 for the piano.

Is Sharri bound to sell her piano to either Mary or Aaron?

Why or why not? Explain your answer