Final answer:
The opportunity cost of attending a concert with a non-refundable, non-transferable ticket is what the individual would have done with their time, not the $50 spent on the ticket.
Step-by-step explanation:
The student's question is about determining the opportunity cost of attending a concert given that they have already spent $50 on a non-refundable and non-transferable ticket. The correct opportunity cost in this scenario includes not just the price paid for the ticket, but also the value of the next best alternative foregone by attending the concert.
Since the sunk cost of the ticket ($50) cannot be recovered and does not affect the decision at the margin, the opportunity cost of attending the concert is not the $50 already spent, but rather what the individual would have done with their time instead of attending the concert. Thus, the correct answer to the student's question is option (a) Zero, plus what I would have done with my time.