This seems more like Fermi estimation (https://en.wikipedia.org/wiki/Fermi_problem). And it is underrated and also it is really hard. I mean, it is easy for the author here to say "look I threw it into Google and it worked" but practically I have seen many people struggle with these sorts of problems - they get the wrong numbers, they divide instead of multiply, or whatever, and the units don't really help.
"divide instead of multiply" is _precisely_ the thing that units help with. If you keep track of them correctly, and you know the units of the result you want, then it's impossible to make that mistake. (Of course there are other errors that units don't catch, but that's a pretty large class of them gone.)
