Answer:
C. By subtracting all the costs from the amount of money the customers paid
Step-by-step explanation:
This would be the easiest and straightforward way to know whether the owners made a profit or a loss (and how much).
Option A is incorrect because charging less or more tax from customers cannot tell anything about profit or loss of any company.
Option B can be a way to increase profit with no information in it about profit/loss
Option D is an advertising strategy with no information on profit/loss of the cafe.