I would like to learn how to design a program that can handle maybe 20 numbers from a list and subtract a number form each one of those 20 numbers.

So if this was my list

12

15

18

11

Then I if could select to subtract 3 from each number to get

9

12

15

8

Ideally I'd like to store these as a list, but for my use case I would need to add all those numbers together ( having the list is just a quick way to cross reference the results with friends).

I messed around with the calculator a bit, but I couldn't anything to work. I appreciate any help! Thanks y'all