6610.4 V considering no current is involved in the 5 V battery in the middle. So consider the two circuits to be separate.
Akash Anand Do we need to assume that? I mean is that not the obvious thing?Sourup Nag Yes, it is... 
865Current is not flowing between B and C because the 5V cell does not have an external closed circuit. If charge flows from one terminal there is no path for it to come back to the other terminal.
53510.4 V because writing KCL at B and C, it shows no current flows from B to C.
Aditya Agarwal but that means, B and C are at same potential.
So how to prove that?Akash Anand Current is not flowing between two points, is that only means that these two points are at the same potential?
I mean is that necessary that if two points are at different potential then current must flow?
Think about it.