I understand that the number of files in a folder must be 15,000 or less.
Is this the same for folders?

Also, how are the number of files in folderA counted in the following cases?

folder A (2 or 20000 ?)
|-- folder B (10000 files in the folder)
|-- folder C (10000 files in the folder)

I'm not good at English, so I'm sorry it's hard to understand.