Formulas depending on which item selected from drop down list

I have created a drop down list with 3 options of profit margins 20,30 & 40. Depending on what is selected I then want to take a net price from a different column and multiply it by either 1.25, 1.4 or 1.6 to get a retail price in another column and cannot figure out how to do this? Columns I refer to highlighted in red