A person climbs up a stalled escalator in 60 ~s . If standing on...

Person's speed walking only is $\frac{1}{60} \frac{\text{ "escalator" }}{\text{ second }}$ Standing the escalator without walking the speed is $\frac{1}{40} \frac{\text{ "escalator" }}{\text{ second }}$ Walking with the escalator going, the speed add. So, the person's speed is $\frac{1}{60}+\frac{1}{40}=\frac{15}{120}\frac{\text{ "escalator" }}{\text{ second }}$ So, the time to go up the escalator ("seconds per escalator") is t=$\frac{120}{5}=$24 $\text{ second }$