List method but keep old filenames

I'm sorry but this is probably an easy question but I can't figure it out. The list method is working great but I need to do a bit more with it than just replace the entire filenames. I tried playing around with the add method but it's not working out.

I have a folder with files like this:
001.jpg
002.jpg
003.jpg

I have a .txt list with filenames like this:
apple.jpg
banana.jpg
orange.jpg

I want this:
001_apple.jpg
002_banana.jpg
003_orange.jpg

So how?

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Nevermind I got it.

So you add the add method and fill in: <name>_

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