Question 1039516
a. 
volume: V
radius: R
height: H

then
{{{V=k*R^2*H}}}
if 
{{{Vnew=2*V}}}
and 
{{{Hnew=H}}} (remains the same), then
{{{Rnew^2=2*R^2}}}
so 
{{{Rnew=R*sqrt(2)}}}

b. 
{{{Rnew=R/2}}}
and 
{{{Hnew=H*4}}}
 

{{{Vnew=k*(R/2)^2*H*4=V}}}
So it remains the same.