Have the answer... need the problem?

Hello everyone.
I have been asked by my boss to work something out??? After an hour, I give up and now defer to you all as the experts and would appreciate assistance.

I have a number - £490 times it by what % to get 345.1264780123p

Basically, the cost for something is 345.1264780123 pence / cents (number to 11 decimal places). We need to know what percentage the original price would be times by what percentage to get to that cost. If I have that calculation, I can take a price list and use the formula to work out what what percentage is taken off to get the cost.

Thanks for ANY help!