I get about 80% down the page to where it says "solutions:" and I feel like I've missed something. went back and read it again, but still missing something. How did we arrive at those numbers? "multiple unknowns" - what kind of math is that? what can I google that will show me how to solve this? I vaguely remember doing problems like this in school but that was a long time ago. I don't even know what this type of math is called.