On Monday, John B. Burr paid $50 for a ticket to concert A on Tuesday night: This concert gives John a benefit of $60. The ticket is nonrefundable and cannot be sold. On Tuesday morning, John learns that there is another concert B at the same time that will give him a benefit of $70 and costs $45 for a ticket. What is John’s opportunity cost of going to concert A? Concert B? Which one should he go to?