How are Open Plan Office areas classified in terms of the Sound Transmission section?

I am trying to determine what composite STC/NIC to design for at areas that are adjacent to Open Plan Office areas (with "cubicle" type workstations).

For example:

If you classify Open Plan Offices as "Collaborative / multi-use" the requirement is STC-45 at adjacency with "Private" offices. If you classify Open Plan Offices as "Hallway, stairway" the requirement is STC-35 at adjacency with "Private" offices. 

Which of the above is correct? Or is it none of the above?