conditional, variable formula

[stevedork]

Thanks for your help last time. What I could really do with is this:
=IF(F4>0,F4*3.4%+0.2,"") but I need to be able to make it either 3.4% OR 3.9%. What I thought was if I use another cell, say F3 which I can leave blank or put a 1 in, and tell it if it has a 1 it is 3.9% + 0.20 or if F3 is blank then it is 3.4% + 0.20
Sorry to be a pain but it is just beyond me, thanks in anticipation.
Steve

[NBVC]

Try then

=IF(F4>0,F4*IF(F3=1,3.9%,3.4%)+0.2,"")

or

=IF(F4>0,F4*CHOOSE(F3+1,3.4%,3.9%)+0.2,"")

[martindwilson]

=if(and(f4>0,f3=""),f4*3.4%+0.2,if(and(f4>0,f3=1),f4*3.9%+0.2,""))

[stevedork]

It really is kind of you to give your time and expertise like this, thanks
Steve