Answer:
An enforceable contract exists, because Downes wired Woods the cancellation after he had mailed the signed contract. Downes signed the contract on June 3rd and mailed it that day, and the cancellation was made on June 4th. It doesn't mater if the mail with the written contract was received at a later date, the date that matters is when the mail was sent (June 3rd).
Therefore, Woods is entitled to purchase the land and Rockwell Realty is entitled to a sales commission.