Airspeed question

[Saabslime]

Going into class C airspace, at what point does the 200 knot restriction come into play? I thought it was within 4 miles of the primary airport but an FO I had the other day seemed to think it was within 10 miles.
I seem to have misplaced my AIM so any replies helping to refresh my deteriorating memory are greatly appreciated.

 

[StormChaser]

I'll reference 91.117(b), since the AIM isn't considered regulatory in nature:

In Class C and D airspace, the 200-knot restriction comes into play within 4 NM of the primary airport provided you are at or below 2500' AGL.