You should not have to do any math "at all" to set your margins. Your printer does not tell you what your margins should be...you establish your margins for your document how you want it to appear. If your printer rejects your margins, you probably have them set too small anyway. Generally speaking, most printers will accept any margins of 0.5" and above on all sides.

And, yes, there are multiple resources out there for help regarding Word. For instance: http://www.addbalance.com/usersguide...m#Page%20Setup will help with setting up your margins (if you have not already seen this). Of course, there are other links such as Basic concepts of Microsoft Word: An introduction | ShaunaKelly.com (pay attention to the links on the left-hand side of the page.