I would like to make exactly 30% on original cost.

Basically, I would like to know if it is even possible to calculate original cost +30%, add the fees and spit out a number that is exactly 30% profit on original $X investment after percentage fees?

I have searched Google and many forums but the only one that comes close is “(ITEM COST+EBAY FIXED+SHIPPING+(1-PROFIT))/(1-EBAY %)” However, when the price changes the profit is sometimes more and sometimes less than 30% and it seems that the (1-profit) just adds 70 cents.