The equivalent capacitance is Ceq=C1C2C1+C2=2×82+8=1.6μF.
Equivalent charge is Qeq=CeqV=1.6×10−6×300=4.8×10−4C
As the capacitors are in series so charge on each capacitor is Qeq=4.8×10−4C.
The potential difference across C1 is V1=QeqC1=4.8×10−42×10−6=240V
The potential difference across C2 is V2=QeqC2=4.8×10−48×10−6=60V
Energy stored in the system is U=12CeqV2=12×1.6×10−6×(300)2=7.2×10−2J