Question

Instead of attending class, one could have worked an extra hour at the café for $10 or watched a neighbor’s child for $15. the opportunity cost of attending class is:

Answer 1

The opportunity cost of attending class is the $15 that could have been made by watching a neighbor's child.
Opportunity cost refers to the benefits that one gives up in order to enjoy another benefit, that is, the benefit that is sacrificed.
In this question, two benefits are given up, but the real opportunity cost is the one that have the highest value, which is the $15.