dfsa

To find the moment of inertia of the remaining disc let us find the mass of the remaining disc and the centre of mass of this portion. So the entire mass of the cut disc can be assumed to be concentrated at this point.

The mass of the cut disc ,m = mass of disc - mass of cut portion = M- M/pi(a)²(pi(b)²  ) = M(b² /a²⁾

Mass of remaining portion, M' = M - M(b² /a² )

Centre of mass of remaining portion can be found out by taking a mass of -m at the portion that is cut out.

So centre of mass = [0- m(c+b)]/[M' - m)]

then use the formula for MI and find it, in case of a difficulty do write in to me.