When adding or subtracting deelmals, how many digits should the answer contain?

Depends, but in most cases, 2.

It's best to use as many digits as possible to keep it accurate.

Explanation:

This varies between teachers, as most schools go with 2 decimal places.

This is something that depends in your situation.

You technically want as many decimals as possible to keep it as accurate, but most people stick with 2.

I personally do 3, and commonly do 5 sometimes.