Please help me with the following example: An air$-$filled parallel$-$plate capacitor has plates of area $3\mathrm{.}2$cm$2$ separated d$=2\mathrm{.}5$mm$.$

a$)$Find the value of its capacitance.

b$)$ Then is connected to a $12$ volts battery,

What is the Energy stored in the capacitor?