Three very large plates are given charges as shown in the figure. If the cross –sectional area of each plate is the same, the final charge distribution on plate C is
 

Inside the conductor field E = 0.
 

Field due to induced charges will be reduced to zero.
$\begin{array}{l}{\overrightarrow{\mathrm{E}}}_{\text{inside }}=\frac{\mathrm{Q}}{{\mathrm{ϵ}}_0\mathrm{A}}+\frac{-5\mathrm{Q}}{{\mathrm{ϵ}}_0\mathrm{A}}+\frac{\mathrm{q}}{{\mathrm{ϵ}}_0\mathrm{A}}-\left(\frac{10\mathrm{Q}-\mathrm{q}}{{\mathrm{ϵ}}_0\mathrm{A}}\right)=0\\ \Rightarrow -5\mathrm{Q}+\mathrm{q}-10\mathrm{Q}+\mathrm{q}=0\\ \Rightarrow \mathrm{q}=7\mathrm{Q}\\ \Rightarrow \mathrm{q}\text{'}=(10-7)\mathrm{Q}=3\mathrm{Q}\end{array}$
q =7 Q  at inner surface
(10 - q) = 3Q  at outer surface