A solid sphere of radius a$=2\mathrm{.}00$ cm is concentric with a spherical conducting shell of innerradius b$=2\mathrm{.}00$a and outer radius c$=2\mathrm{.}40$a$.$ The sphere has a net uniform charge q$1=5\mathrm{.}00$ fC;the shell has a net charge q$2=$q$1.$ what is the magnitude of electric field at radial distances r$=2\mathrm{.}3$a$?$