Adam decided that he did not want to go thru with the deal. In light of his contractual obligation to buy the shoes, Adam spoke to his friend Shane who was an Elvis freak and convinced Shane to take his place in the deal. Steven said that that was fine with him. In this example, Adam's performance is said to have been:

a) Breached

b) Discharged by agreement of the parties (substituted party)

c) Discharged by operation of law

d) Discharged by frustration of purpose