) compressed archive, likely a movie or media content, that has been compressed using RAR software, with "R-MG" often indicating the release group.
You will need tools like WinRAR or 7-Zip to extract this archive.
If you only have part 13, you cannot extract the file. You must have all parts present in the same folder. To help you further, could you let me know: Where did you find this file name (a forum, tracker, etc.)?