Delete multiple files at once

[Android Central Question]

I just realized there are 4,000 .txt files saved on my Zenpad 8. It seems some apps cause a .txt files to be saved to documents every time they're opened, what are these? Anyways, I want to delete these and there are 4,000 of them so checking each one is not an option. Is there a way to delete all .txt files at once?