A parallel$-$plate capacitor has plates with an area of $450$ cm$2$cm$2$ and an air$-$filled gap between the plates that is $2\mathrm{.}50$ mmmm thick. The capacitor is charged by a battery to $600$ VV and then is disconnected from the battery. How much energy is stored in the capacitor? How much work is required to increase the separation of the plates from $2\mathrm{.}50$ mmmm to $4\mathrm{.}40$ mm