There are numerous ways to do this:
Here is Tim' remix of an old tutorial (Pizza Party) https://groups.google.com/g/mitappinventortest/c/hOx-n14lkBs/m/Nq2OIuyAAQAJ that could be used as the basis for the app. Use the Math Blocks to variously provide deductions of 5 and 10 percent.
Here is an app in the MIT Gallery MIT App Inventor Gallery . It might be the basis for your Project. If not, search within the gallery for restaurant or bill perhaps.
Here is another example discussed from the old forum .
I added discount Buttons.
This app does not use a list; it uses checkboxes to select food items.
Fish_Fry_10.aia (14.1 KB)
