How many speakers do I have? Any suggestions regarding no sound from rears with stock non Bose HU and no amp.

[scomis]

I just bought a 2009 Tahoe LT with a non-Bose stock head unit and no amp I think. I was wondering how many stock speakers came in the truck? I assume driver and passenger doors, but are there any in the D pillars on the base stereo any in the front pillars? The reason I ask is that I only have sound from the front speakers. When I put the fader to rear, it is silence. My rear audio controls seem to work. They turn on and off and the headphone jacks play music. I pulled the head unit to make sure the plugs were firmly in and that couplers were connected. The previous owner is a friend and said that they had not heard any speakers going out and didn't even realize that the rears were out.