Answer: Jill is incorrectly ignoring the opportunity cost of using the building she owns.
Step-by-step explanation:
Based on the information given, Jill is incorrectly ignoring the opportunity cost of using the building she owns.
Here, opportunity cost refers to the cost of what an individual forgoes when such person decides to choose another alternative. Even though he thinks that he's paying no cos for the restaurant, he actually does through the opportunity cost.