imc

Let $s$ be the speed of the escalator and $c$ be the speed of Clea. Using $d=vt$, the first statement can be translated to the equation $d=60c$. The second statement can be translated to $d=24(c+s)$. Since the same distance is being covered in each scenario, we can set the two equations equal and solve for $s$. We find that $s=\frac{3c}{2}$. The problem asks for the time it takes her to ride down the escalator when she just stands on it. Since $t=\frac{d}{s}$ and $d=60c$, we have $t=\frac{60c}{\frac{3c}{2}}=40$ seconds. Answer choice $\boxed{40}$ is correct.