Sharing of Charge between Capacitors

2022 1 question

1. A capacitor of capacitance $C=900\ pF$ is charged fully by 100 V battery B as shown in figure (a). Then it is disconnected from the battery and connected to another uncharged capacitor of capacitance $C=900\ pF$ as shown in figure (b). The electrostatic energy stored by the system (b) is