Formula for shopify custom calculator

Hello, I am adding a custom calculator to our shopify store so that customers can get a instant price on the length and depth of shelving. The calculator users formula and I have managed to create one but it needs to be nested. It uses if then else. i.e ((Depth<= 140)?(Length*0.11):(0)) I have a spreadsheet of all the sums. I cant get nesting to work. Thanks alot i think it will be quite for someone advanced in excel