Question 1018215
.
It is well known fact that the volume of the cylinder of the radius R and of the height R minus the volume of the hemi-sphere 
of the radius R equals the volume of cone of the radius R and the height R.


I.e. equals one-third of the volume of the cylinder.


Well known after Archimedes. 


See the picture in

<A HREF=http://mathcentral.uregina.ca/qq/database/QQ.09.01/rahul1.html>http://mathcentral.uregina.ca/qq/database/QQ.09.01/rahul1.html</A>


So the answer to question B) is: {{{1/3}}} of the height of the cylinder, which (height) is 2R.


Without any calculations. Simply refer to Archimedes.