$13\mathrm{.}7$ Consider a parallel$-$plate capacitor having an area of $2500$ mm$^2,$ a plate separation of $2$ mm$,$ and a material of dielectric constant of $4\mathrm{.}0$ positioned between the plates. $($a$)$ What is the capacitance of this capacitor? $($b$)$ Compute the electric field that must be applied for $8\mathrm{.}0$ x $10-9$ C to be stored on each plate