This goes for all of these problems you're sending in. First, if you see the big RED notice at the top of the page, homework is supposed to go over to the homework section under Education. If you go over there, there's another notice stating to send in any work you have done or ask general questions about how to do something, as we are not here to just answer your homework for you. All you keep sending in are problems and nothing else. I can help start you off or give hints, but I like it much better when I see your attempts to do your own work first.
Margin of safety is just how much sales exceed break even. To get anything as a percent, you divide the first by the second. i.e. You have a 50 point test and you got 45 points. What percent is 45 Of the 50. That's a division in order: 45/50. Always works. And anything that says "ratio" is essentially the same math: divide in order.