Answer:
They should give out a coffee cup to each person and charge full price for the first time that you fill the cup but then after they finish the first drink they should offer a discount if you reuse the same cup. They should tell you that you can bring back coffee cups from even a few days ago and you could still be eligible for the discount. This way even people that don't drink as much coffee can still be eligible to get a discount on their coffee.
Step-by-step explanation:
:)