Answer: a. $18,000
Step-by-step explanation:
Economic costs are the sum of opportunity costs and accounting costs incurred when the next best alternative is not followed.
In this case, the opportunity costs are the salary that Jon Brooks foregoes and the actual costs are the cost on books and cough medicine.
Economic costs will therefore be:
= 15,000 + 2,000 + 1,000
= $18,000