Working out sums with dropdown lists

Can someone help!

I have attached a worksheet that I am trying to get a formula to work which will basically insert a value in the proffit column, depending on what is chosen in the Phone and tariff column.

The handset cost, and tariff commission is in a seperate worksheet, and I want the tariff column to work out the commission less the cost of the handset chosen in the main worksheet! Complicated?

Daily's Test.xls

Excellent!! Thankyou so much!