3. (a) That's right. We have already seen that B has created a binding contract of purchase and sale between A and C. And, when B pays C, he is doing so on behalf of A, so it is as if A has himself paid C. It is therefore correct to say that B has discharged contractual obligations on behalf of A.

As a result of what B has done as his agent, A is now entitled to sue C for delivery of the machine he has bought from C and already paid for.