\(k _{ sph }=\sqrt{\frac{2}{5}} R\)
For solid cylinder \(\frac{ mR ^2}{2}= mk _{ cyl }^2\)
\(\Rightarrow k _{ cyl }=\frac{ R }{\sqrt{2}}\)
\(\frac{ k _{ rph }}{ k _{ cyl }}=\frac{\sqrt{\frac{2}{5}}}{\frac{1}{\sqrt{2}}}=\frac{2}{\sqrt{5}}=\frac{2}{\sqrt{ x }}\)
\(\therefore x =5\)