So tonic chord in first inversion or Ib in roman, with 5/7 being dominant chord in 3rd inversion or Vc in roman.
Somewhat confusingly, but ultimately way easier for bassists, 5/7 would be the first inversion of the 5 chord.
The numbers are always going to relate to major scale intervals. So in the key of C 5/7 would be G/B chord. If you wanted to have the G chord in 3rd inversion it would look like this 5/4.
Basically read every number as it relates to the tonic or 1 chord, unless it’s a small number next to it used to indicate a specific voicing like on a standard lead sheet.
So a dominant 5 chord would have a little seven on the upper right hand side and no slashes in between them.
I’m a fan generally!