Which formula gives the energy stored in a charged capacitor?

Energy per unit volume for a capacitor having area $A$ and separation $d$ kept at potential difference $V$ is given by

The total energy stored in the capacitor system shown in the figure will be (in $\mu J$)

$A$ variable condenser is permanently connected to a $100 \ V$ battery. If the capacity is changed from $2 \ \mu F$ to $10 \ \mu F$,then the change in energy is equal to:

If $C$ is the capacitance and $V$ is the electric potential,then the dimensional formula of $C V^{2}$ is

If the charge on the capacitor is increased by $2 \text{ C}$, the energy stored in it increases by $21 \%$. The original charge on the capacitor is (in $\text{ C}$)