If I enter 1 in column A I'd like column B to increase by $20.50.
If I enter 2 in column A I'd like column B to increase by $9.70
If I enter 3 in column A I'd like column B to increase by $4.30
If I enter anything else in column A I'd like column B to decrease by $6.50

I assume I can't do that with a simple formula so how would I go about it?