I need a formula that will give me the selling price. I have the cost of the
product and I want a formula I can plug in a profit margin to get the selling
price. Ex:

My cost is $3.98. I want a 40% GPM. The selling price should be $6.63

I have tried =((1-I5)+1)*E9, where I5 is the plug in GP percentage and E9 is
the product cost, but this gives me $6.37, which is a 38% GPM. Is this the
best I can expect - close but not exact?