Step-by-step explanation:
Elevator's starting point = -90ft
Elevator's position after 15s = -20ft
The elevator did move upwards as
-20ft. > -90ft.
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Distance covered by the elevator = -20 + -90
= -20 + 90
= 70ft.
Time = 15s
Speed = distance/time
= 70/15
= 4.7ft/s
