Isidore Goresky wrote:

I want to burn a CD (700MB) for an old 2002 car cd player for a friend.
I have about 30 MP3 files (150MB).

ImgBurn is asking to choose between iso9660 udf or joilet.

Which do I pick?

ISO 9660 and Joliet are for data discs. Not all car audio players of
that era can read them. Unless you're sure that "old 2002 car cd player"
supports MP3 discs, you're better off with CD-DA (audio CD).