A silicon$-$based MOSFET has a square gate $0\mathrm{.}50$ m on edge. The insulating silicon oxide layer that separates the gate from the p$-$type substrate is $0\mathrm{.}20$ m thick and has a dielectric constant of $4\mathrm{.}5.($a$)$ What is the equivalent gate$$substrate capacitance $($treating the gate as one plate and the substrate as the other plate$)?($b$)$ Approximately how many elementary charges e appear in the gate when there is a gate$$source potential difference of $1\mathrm{.}0$ V$?$