Can you help me in this question?

The opportunity cost will be "Work in the local library".

Step-by-step explanation:

Opportunity cost is the cost of next best alternative.

There is case :

Henry wants to get a job this summer.

He can either mow lawns or work in the local library.

But if he decides to mow lawns.

Then the next best alternative would be "Work in the local library".

Hence, The opportunity cost will be "Work in the local library".