Hi mate,
I guess the word you are looking for is subtraction. Maths does that with ease. Maybe you want to look at this fine piece of work that someone put together...
Maths illustrated supplement (Page 15 should be about right)

In my opinion it's a must read for maths users. On the other hand there is the Addac 216 that has the subtitle sum&difference. If you fancy a dedicated module for that purpose.

Have fun