Theorem of Parallel Axes

The axis is normal to the disc and passes through a point on its edge (the end of a diameter).
Moment of inertia of the disc about the axis through its centre and normal to its plane: $I_1 = \dfrac{1}{2}MR^2$
The required axis is parallel to this axis and at a distance $R$ from it.
By the theorem of parallel axes: $I_2 = I_1 + MR^2$
$I_2 = \dfrac{1}{2}MR^2 + MR^2$
$I_2 = \dfrac{3}{2}MR^2$

Moment of inertia of the disc about the axis through its centre and normal to its plane: $I_{cm} = \dfrac{MR^2}{2}$
The required axis passes through the edge and is parallel to this axis, at a distance $d = R$ from it.
By the theorem of parallel axes: $I = I_{cm} + Md^2$
$I = \dfrac{MR^2}{2} + MR^2$
$I = \dfrac{3}{2}MR^2$