how is it 2R2? Confused now, as the solution that was provided for the problem I mentioned in previous post, we used the Ad I posted. With Acm=0, so would Acm=0 here?

I keep telling you to look on the internet:
http://www.allaboutcircuits.com/vol_3/chpt_8/10.html
http://en.wikipedia.org/wiki/Instrumentation_amplifier
http://www.intersil.com/data/an/an1298.pdf

Common mode gain is a function of R3 and R4. If both R3's are truly equal, and both R4's are truly equal, and the op amps are ideal (infinite CMRR), then the common mode gain will be zero.

 

The OP needs to post his circuit in order to obtain any assistance. He should also be aware that deleting the original question is not in keeping with the spirit of these forums - http://forum.allaboutcircuits.com/showthread.php?t=51179