Correct answer is : 12
\(k_{eq} = \frac {2k.k}{3k} + k = \frac {5k}{3}\)
Angular frequency of oscillation \((\omega)=\sqrt {\frac {k_{eq}}{m}}\)
\((\omega)=\sqrt {\frac {5k}{3m}}\)
Period of oscillation \((\tau)=\frac {2\pi}{\omega}=2\pi \sqrt {\frac {3m}{5k}}\)
\(=\pi \sqrt {\frac {12m}{5k}}\)
