Answer
At a specific height $s$, the wind speed is $75\%$ of the maximum eyewall wind speed $v_0$.
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Work Step by Step
$r(s)$ represents the wind speed at height $s$.
$v_0$ is the maximum wind speed, which occurs at height $s_0$.
In $r(s)=0.75 v_0$, the variable $s$ is the height (or heights) at which the wind speed is $75 \%$ of the maximum wind speed.
