Hello fardeen_genYou need the formula for the period of oscillation of a compound pendulum, which is:

where is the moment of inertia about the axis of rotation

is the mass

is the distance of the centre of mass from the axis of rotation

The moment of inertia of a rod of mass , length about one end is , and the moment of inertia of the bob is , so

Total mass =

and, taking moments about the axis of rotation:

(I think you have some brackets missing in your answer!)

Grandad