... and found this. I hope it will do the job, but I don't understand the last bit (Assuming anyone understands what I've written here). ADMARSH has graciously been assisting me in typing formula in a way that might be readable.

The part I don't get (I am definitely NOT particularly good at formulas) is the bit. It seems to indicate to me that the result of the bracketed expression then gets cubed then squared, or that's how it looks to me. But I'm probably talking rubbish. Can anyone advise, please?