What's a possible opportunity cost when you spend $100 on a pair of sneakers?

Opportunity cost : the cost of an alternative that must be forgone in order to pursue a certain action

in this case, let's say that you use that $100  to buy a X-brand of sneakers. meanwhile there's Z-Brand sneakers, another alternative brand with same quality but it only cost $95, but you do not know about it. Which mean, you just loss $5 worth of opportunity cost

The letter c i’m pretty sure

How can we answer it? we need more info on the question lol.