
Moment of inertia of the solid sphere about any diameter is given by, 52m1R2.
Using parallel axis theorem, we get
Isolid sphere =52m1R2+m1R2=57m1R2
=57×5R2
=7R2

Moment of inertia of the disc about the diameter is given by, 4m2R2.
Now using parallel axis theorem, we get
Idisc =4m2R2+m2R2=45m2R2
=45×4R2
=5R2
Therefore,Isoild sphere Idisc =75
Thus, x=5.