Want To Add Percentage To Number [closed]

I Am Working In Project Required Online Payment Service And My Clients Will Pay The Cost Of Service (Online Payment) , My Provider Rate Is 2%

For Example
My Client Want To Pay 500 EGP , Now When I Put 2% On The Amount Will Be 510 EGP But I Still In Trouble Because My Provider When He Judges Me Will Put The 2% On 510 EGP Not 500 EGP And The Cost Will Be 10.2 EGP NOT 10 EGP

Can Anyone Help My Out !!

When I Tried It’s Not Working As Expected