[a1369209993]

  $ units
  You have: 25m2 / 2tau(700km)^2
  You want: /billion
    * 0.0040600751
    / 246.30086

[ben_w]

The 'units' command line tool has been part of Unix since Bell Labs, and GNU Units came along in 1997.

Personally I used basic high school geometry knowledge of "what's the area of a sphere", and you could also have just asked WolframAlpha, which also predates LLMs.