I purchased a B tag for rifle season for elk and specified unit 4. Can I hunt in unit 9 also?

Yes, Unit 4 is in a zone that included Units 1, 2, 3, 4, 4A, 5, 6, 7, and 9.  You could have used a rifle to take an antlered elk in any of those units from October 10 - 24 using your B tag.   F08