Answer:
The average speed of the elevator going down in the abandoned mine is 17.722mph.
Explanation:
If the elevator takes 90 seconds to descend a height of 713m, the average speed of the elevator is:
[tex]v_{av}=x_T/t_T=713m/90s=7.922m/s[/tex]
And if 1m/s is 2.23694mph, the average speed is:
[tex]v_{av}=7.922m/s=17.722mph[/tex].