What are two benefits of choosing a formula held instead of an Apex trigger to fulfill the request?

A develop created these three roll-up summary fields on the custom object. Project_c:

The developer is asked to create a new field that should the ratio between rejected and approved timesheet for a given project.

What are two benefits of choosing a formula held instead of an Apex trigger to fulfill the request? Choose 2 answers
A . A test class will validate the formula field during deployment.
B . A formula field will trigger existing automation when deployed.
C . A formula field will calculate the retroactively for existing records
D . Using a formula field reduces maintenance overhead.

Answer: B,C