
Moment of inertia of solid cylinder of radius R and length L about the axis is I1=2M1R2.
Moment of inertia of carved out portion of the cylinder of radius 2R and length 2L is I2=2M2(2R)2=8M2R2
Now, the ratio I2I1=M24M1
As, mass=density×volume
So, I2I1=4×2ρπR2L4×ρπR2L=32