Excel formula for reverse percentage calculation

Question

I have a calculation which I am unable to crack.

Lets say my Cost Price is 300. I want to sell the item at No Profit or No Loss. My total commission/expenses will be 30%. So it means i need to sell the item at 390. But if I do 390 - 30% = 273.

How can I see the item, so that if I minus 30% to it. My Revenue will still be 300.