(b) That's not right. Sometimes reaching agreement takes a lot of negotiation. In other cases very little discussion is needed before the parties are ready to contract. Whatever the case, the stage must be reached where the parties clearly signal that they are finished negotiating and are ready to contract on particular terms. This process is often described as 'offer' and 'acceptance'.

In this case A seems to be clearly indicating a readiness to contract on the stated terms. As between A and B, this is the first indication of such readiness, so A's statement is called the offer. B's reply, which also indicates a readiness to contract on the offered terms, is the acceptance of the offer. When there is offer and acceptance, we can conclude that the parties have reached agreement.

Note: A person making an offer is referred to as the 'offeror'. The person to whom an offer is made is called the 'offeree'.