Excel Combo Box and VLookUP

[justmccarthy]

What I want is if user selcts say Data from combo box in a cellC19 and then enters a number value like 400 into K19 then Cell O19will equal K19*0.2 to give value in O19 else user may enter value in L19 and if so then I want L19*0.5 to then equal O19 say just for example
But I want this for all cases in the combo Box i.e I have 10 cases
How will I do this for all cases..
Also if user enters value in either K19 or L19 is there a way so he can not enter in both just one entry
See attached file