An electron is to be accelerated in a uniform electric field having a strength of$1\mathrm{.}40106$V$/$m$.($a$)$What energy in keV is given to the electron if it is accelerated through$0\mathrm{.}420$m$?$keV$($b$)$Over what distance $($in km$)$ would it have to be accelerated to increase its energy by $50\mathrm{.}0$ GeV?$$km