Ok, so V6 is 1st and V64 is 2nd Inversion... but why 6 and 4?

I would be remiss if I didn’t chime in here to mention that this is also covered in our book :slight_smile:

http://www.hooktheory.com/music-theory-for-songwriting

Relevant graphic from Chapter 5.1

Book 2 will cover seventh chords and their inversions.

-Dave