A very long charged solid cylinder of radius $a$ contains a uniform charge density $\rho$. Dielectric constant of the material of the cylinder is $K .$ What will be the magnitude of electric field at a radial distance $x\left(x<a\right)$ from the axis of the cylinder ?

Consider a region in free space bounded by the surfaces of an imaginary cube having sides of length $a$ as shown in the figure. A charge $+Q$ is placed at the centre $O$ of the cube. $P$ is such a point outside the cube that the line $OP$perpendicularly intersects the surface $ABCD$ at $R$ and also $OR=RP=a/2$. A charge $+Q$ is placed at point $P$ also. What is the total electric flux through the five faces of the cube other than $ABCD?$