I am using a 2012 27in. MAC running OS 10.8.5. I have a powerpoint presentation that I want to show on two different projectors. I can project it on the front projector, but can't get it to show on the rear projector. I want the speaker that is using their powerpoint presentation to be able to see what they are showing on the rear screen without having to turn around to see what's on the front screen. I am not a MAC (apple) user so any response needs to take that into consideration. I have searched for answers but have not been able to find a suitable explanation. Please help.