WBJEE 2018 Physics Solved Paper

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