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

Answer 1

the formula you want is

=300/0.7

or

=300/(1-30%)

basically it is 300= x*(1-.30) where the (1-.30) is the amount that wants to be kept after the commision of 30%. Solving for x we get the above formula.