How to rename multiple folders that have a set number of files within that folder using batch script?

I am very new to programming so your help is much appreciated!

I have a top directory, containing subfolders which have files in them. I want to add the string "x" after the folder name e.g. foldername -> foldernamex if the subfolders contain less than 4 or greater than 4 files. How do I go about doing this?