Hi! I recently came accross this pic: Problem is, I have no clue how to tackle this. I didn't find it in any textbooks or anything, so I don't know where to look for it. Sorry if it's a "weird" question, but it's been eating at me for a couple of hours now. I saw it categorized as "high school algebra", but I don't remember seeing this anywhere, so I'm a bit at a loss (I'm not based in the US though, so I guess there's that to take into account). A link to a wikipedia article or something would be nice, but any help is appreciated!