At resonance, frequency of walking $=$ Frequency of oscillation

$f _{\text {milking }}=\frac{ v }{\ell}$ (where $\ell$ is length of step \& $v$ is velocity)

$\Rightarrow \frac{ v }{\ell}= f _{ osc. }$

$f _{\text {osc. }}= kh ^5 R ^y g ^2( k$ is dimension less constant)

By question,

$x =\frac{1}{2} \Rightarrow T ^{-1}= L ^{\frac{1}{2}} L ^v\left( LT ^{-2}\right)^{z}$

$\Rightarrow z =\frac{1}{2}, y =-1$

$\Rightarrow \frac{ v }{\ell}= k \sqrt{ h } R ^{-1} g ^{\frac{1}{2}} \Rightarrow v \propto \frac{1}{ R }$