D$2\mathrm{.}2.$ A charge of $0\mathrm{.}3\backslash$mu C is located at A$(25,30,15)($in cm$),$ and a second

charge of $0\mathrm{.}5\backslash$mu C is at B$(10,8,12)$ cm$.$ Find E at: $($a$)$ the origin; $($b$)$ P$(15,20,$

$50)$ cm$.$