its easy juzz solve the circuit first
to find equivalent capacitance..
find the total charge stored..
and also charge on each capacitor...
find charge on capacitor btwn terminals a and b
Q=48/11
C=4uF (given)
So V=Q/C =48/911*4)....V=12/11
juzz keep in mind that..in parallel voltage remains the same...and in series charge remains the same..