Fig. shows a uniform solid block of mass M and edge length a, b and c. The moment of inertia of the  block about an axis through one edge and perpendicular (as shown) to the large face is

The moment of inertia about centre of gravity is given byIC.G.=Ma2+b212To obtain the moment of inertia about the required axis, we apply the theorem of parallel axes, henceIrequired axis =IC.G.+M(OA)2=Ma2+b212+Ma2+b24=Ma2+b23