How to price product

[sanok]

Example:
lets say I would like to have $100 in my pocket after the sale. But Ebay + Paypal fees are 13.2% of the final sale price, so I need to add 13.2% to my $100, thus my final sale amount becomes $113.2 Now deducting 13.2% from this amount will give me less than $100 ($98.25).
By a trial and error I've found a percentage by which my $100 has to be increased in order to get $100 after the fees. That percentage is roughly 15.21%, $100+15.21%=$115.21, $115.21-13.2%=$100.002. So from the above example it looks like I have to increase the 13.2% by 2.01 to get 15.21% (by which I have to increase my sale price). However this 2.01 increase only applies to 13.2%. If 13.2% is changed to any other number the above calculation won't work.
What is a proper math formula to calculate something like that, so it can apply to any percentage?
thanks for any help

 

[stapel]

Let's say I would like to have $100 in my pocket after a sale. But Ebay plus Paypal fees are 13.2% of the final sale price, so I need to add 13.2% to my $100....

No. You are correct that $13.20 is 13.2% of $100. But then $13.20 cannot possibly also be 13.2% of $113.20.

To learn how to set up and solve "percent of" exercises, try here. Once you have learned the basic terms and techniques, please attempt this exercise again. If you get stuck, please reply showing all of your efforts, starting from the variable you picked for the unknown selling price. Thank you!