$\Rightarrow \mathrm{ma}=-\rho \mathrm{g} \mathrm{Ax}$
$\Rightarrow \mathrm{a}=-\left(\frac{\rho \mathrm{g} \mathrm{A}}{\mathrm{m}}\right) \mathrm{x}$
$\Rightarrow \omega_{\text {cylinder }}=\sqrt{\frac{\rho g A}{m}} \ldots(i)$
$\Rightarrow \omega_{\text {spring -block }}=\sqrt{\frac{\mathrm{k}}{\mathrm{m}}}$ $...(ii)$
$\Rightarrow \omega_{\text {cylinder }}=\omega_{\text {spring - block }} \ldots$ $(iii)$ $[given]$
$\Rightarrow \mathrm{K}=\rho \mathrm{g} \mathrm{A}[\text { from }(\mathrm{i}),(\mathrm{ii}),(\mathrm{iii})]$
$\mathrm{K}=27 \mathrm{N} / \mathrm{m}$

