hemisphere

Let the diameter= 2r

So radius=r

According to question,

 the height of the bulding above thee floor=diameter=2r

radius of the hemisphere=r(as it's mounted on the cylinder)

This shows that height of the cylinderical part =r

solve this by equating the given volume with the volume we have found.

This will give you the value of r

Height of the building also=r

That will give you the required answer.