D$3\mathrm{.}2.$ Calculate D in rectangular coordinates at point P$(2,3,6)$ produced by: $($a$)$ a point charge QA $=55$ mC at Q$(2,3,6)$; $($b$)$ a uniform line charge LB $=20$ mC$/$m on the x axis; $($c$)$ a uniform surface charge density SC $=120$C$/$m$2$ on the plane z $=5$ m$.$

Ans. $($a$)6\mathrm{.}38$ax $9\mathrm{.}57$ay $+19\mathrm{.}14$az $$C$/$m$2$; $($b$)212$ay $+424$az $$C$/$m$2$; $($c$)60$az $$C$/$m$2$