b
In $SHM,$ velocities of a particle at distances $x_{1}$ and $x_{2}$ from mean position are given by
${V_{1}^{2}=\omega^{2}\left(a^{2}-x_{1}^{2}\right)}...(i)$
${V_{2}^{2}=\omega^{2}\left(a^{2}-x_{2}^{2}\right)}...(ii)$
From equations $(i)$ and $(ii),$ we get
$V_{1}^{2}-V_{2}^{2}=\omega^{2}\left(x_{2}^{2}-x_{1}^{2}\right)$
$\omega=\sqrt{\frac{V_{1}^{2}-V_{2}^{2}}{x_{2}^{2}-x_{1}^{2}}} $
$T=2 \pi \sqrt{\frac{x_{2}^{2}-x_{1}^{2}}{V_{1}^{2}-V_{2}^{2}}}$