Let the retail price be 100.
Discount = 15
and Selling price = 85
So, Cost price =\(\frac{85}{1.02}=\frac{500}{6}\)
To achieve a profit of 20%, the selling price needs to be \(=\frac{500}{6}(1.2)=100\)
To achieve a profit of 20%, the seller needs to sell at the retail price.