This solution uses a docker to remove the need for system level dependencies. You'll need a computer with the docker service and command working.

1. make build to build the docker image.
2. make run term=12 amount=2404 to run the calculation.
3. make test to run tests

• The responsibility for validating an Application could be handled by a separate service, not by FeeCalculators.
• Converting numerical inputs (floats) to integers may have made it easier to avoid issues with precision when performing calculations, especially as bcmath expects strings for inputs/outputs.
• Perhaps I could have used a pre-built 'event bus' and conformed to a better known design pattern.

Test instructions