Hi there!
In order to solve, we'll need to use a proportion: 20/a = 21/20. Then, we'll cross-multiply and solve to find a: 21a = 400 | a = 19.05. Next, to find b, we can just use pythagorean theorem: 20^2 + (400/21)^2 = b^2 | b = 27.62.
We are using geometric mean to solve for a, then using pythagorean theorem to solve for b. If you need more help with geometric mean, or would like a complete explanation, please let me know! I'd be happy to provide you with that information.
Hope this helps!! :)
If there's anything else that I can help you with, please let me know!