the opportunity cost of a worker going to the university  is

Explanation

Opportunity cost is the value of the next best thing you give up whenever you make a decision. It is "the loss of potential gain from other alternatives when onealternative is chosen". it is simply the forgone alternative

If, for example, you spend time and money going to a movie, you cannot spend that time at home reading a book, and you can't spend the money on something else.