Imagine a world where there is more than ONE thing you don’t know. Yes, it’s hard to imagine... but there are problems out there with more than one unknown. Not only that, but sometimes you’ve got one unknown that appears multiple times in the same equation! No worries, though... you already know how to manipulate your equations. Add that knowledge to the tools you’ll learn in this chapter, and you’ll be solving more complicated expressions in no time at all.