script - Search for most recent file under a directory and copy the folder containing it to another directory

In my directory I have many files with the same name also in many other subdirectories

example file structure:

C:\a\first\hello.txt
C:\a\second\hello.txt
C:\a\third\hello.txt

I need to specifically search for the most recently modified 'hello.txt' (as there are also other files in the directory) and copy its containing folder to C:\b

Am very new to batch so explanations would be fantastic :)