Bottom exposure time assurance

Hi, if I have a layer exposure time of 1.40 seconds what should the bottom layer exposure time be? I know it’s supposed to be around 12 times the layer exposure number but JUST to be sure, I’d like other experienced printer people to tell me the number it should be as well so I can get over the fear that maybe my calculator doesn’t know that I’m being specific about certain things. Weird fear, I know I know, but it’d just help to have the assurance from experts. Thanks!