According to this video:
Opportunity Cost of a choice is what you gave up to get it.
Now, let us read the following question:
You are going to a football match next Saturday evening, you have already bought the tickets and cannot resell it. You have just learned that on this Saturday evening, there is also a rock concert that you are interested in. The ticket for the concert costs 40\$ but you value this concert as much as 50\$.
What is the opportunity cost of going to a football match?
a) price of football match’s ticket
My answer was (c). Coz, I gave up the concert which costs 50\$.
However, my teacher says that the correct answer is (d). Why?