(c) $v_{\max} = a\omega = a\frac{2\pi}{T} = \frac{2\pi a}{2\pi\sqrt{\frac{m}{k}}} = a\sqrt{\frac{k}{m}}$
Hence, $\frac{v_{max1}}{v_{max2}} = \frac{a_{1}}{a_{2}}\sqrt{\frac{k_{1}}{k_{2}}}$
$\because$ $v_{max1} = v_{max2}$ (given)
$\frac{a_{1}}{a_{2}} = \sqrt{\frac{k_{2}}{k_{1}}}$