$005,10\mathrm{.}0$ points

Consider a solid conducting sphere with a radius a and charge $Q_1$ on it$.$ There is a conducting spherical shell concentric to the sphere. The shell has an inner radius $b>a,$ outer radius $c$ and a net charge $Q_2$ on the shell. Denote the charge on the inner surface of the shell by $Q_2^{\text{'}}$ and that on the outer surface of the shell by $Q_2^{\text{'}\text{'}}.$

Find the magnitude of the electric field at point $P(||vec(E{)}_P||-=E_P),$ where the distance from $P$ to the center is $r=\frac{a+b}{2}.$