This is a business law question

On May 29, Mr. Green makes an offer to purchase widgets from Mr. White and sends it to him via regular mail. On May 31, Mr. White receives the offer and sends his acceptance to Mr. Green. But Mr. White put insufficient postage on the envelope. One day later o n June 1, Mr. Green revokes the offer by sending a letter to Mr. White through regular mail. Mr. White gets his letter with no postage on it back from the post office on June 2. He then sends the undelivered acceptance via overnight express mail to Mr. Green. Mr. Green receives the overnighted acceptance letter on June 3. The revocation letter reaches Mr White on June 4 Mr. Green argues there is no contract because he revoked his offer. Mr. White argues there is a contract because he accepted Mr. Green's offer before it was revoked. Who is correct? TTT Ariel