Interesting. I was thinking about buying a copy for my grandson, then I saw the 500 dollar price tag. I don’t need math to know that’s too big a number for me.
And obviously I misstated the number in my solution, and left out part of my work. ;~)
https://archive.org/stream/QuickAndEasyMath-English-IsaacAsimov/asimov-quick-maths#page/n7/mode/2up
Hit the gray button in the upper center to download.
You owe me a beer.