What is the difference between a one- and two-variable data table? Provide an example of when you would use a one-variable table, and an example when you would use a two-variable table and describe how they are used as a what-if analysis tool.

I have the answer from the book, but I would like someone to expand on it, please. I asked the same question earlier and didn't get a satisfactory answer so please, Explain as if you're talking to a novice. Thanks