Exchange Rate Fluctuation Adjustment Calculation

Okay, I think this is still unanswered because everyone is unsure of what you are really asking. You state you are not a guru, but your question, as described, seems to be very basic. So basic, that I think people are hesitating in answering for fear that (a) this devolves into an 'Excel for Dummies' discussion (in which case, just get a book or read the many tutorials on line), or (b) there is more to it than meets the eye (e.g. you are looking for a way to automatically grab the latest exchange rates from a website).
So, let me answer it at the basic level and see where this goes...

Yes, excel can certainly perform that calculation. Let's say you have the FCC in cell A1, i0 in cell B1, i1 in cell C1, and Qty in cell D1. In cell E1, you can type:
=A1*D1*(C1-B1)/B1
to get your adjustment.