Call the radius is r, the height is h

We have: 

Cylinder 1 has the volume is: \(\left(2r\right)^2.\Pi.h=\Pi.4r^2.h\)

Cylinder 2 has the volume is: \(r^2.\Pi.k.h\)

We have: \(\dfrac{C1}{C2}=1\)

\(\Rightarrow\dfrac{4r^2.\Pi.h}{r^2.\Pi.k.h}=1\)

\(\Rightarrow\dfrac{4}{k}=1\)

\(\Rightarrow k=4\)