A charge q$1=-2\mathrm{.}80$C is at the origin. A charge q$2=3\mathrm{.}20$C is at x $=20\mathrm{.}0$ cm on the x axis. What is the electric potential in SI units at x $=30\mathrm{.}0$ cm$?$

You attach a $2\mathrm{.}8$F capacitor across a $145$ V battery. How much joules of energy is stored in the capacitor?

A parallel plate capacitor has plates of area $4\mathrm{.}90\backslash$times $103$ m$2$ and plate separation $2\mathrm{.}80\backslash$times $104$ m$.$ The capacitor is filled with a material that has a dielectric constant of $3\mathrm{.}90.$ Determine the capacitance of this system in pF$.($The permittivity of free space in $0=8\mathrm{.}85\backslash$times $1012$ F$/$m$.1$pF $=1012$ F$)$