Answer:
b. Harry did not withdraw his counteroffer in time, so a contract was formed.
Explanation:
Angie's acceptance was placed in the mail before Harry communicated his revocation (Before Harry says he is no longer interested) of the counteroffer. If the mailbox rule (the acceptance of an offer takes place when communicated) applies, in this case, it means that Angie's acceptance was effective and a binding contract was formed. (also know that there are some exceptions to the mailbox rule example, some purchase agreements used all the time states that the mailbox rule does not apply)