Answer: The elevator takes 20 seconds to travel from first floor to sixteenth floor.
Step-by-step explanation: Given that an elevator takes 4 seconds to travel from the first floor to fourth floor.
We are to find the time taken by the elevator to travel from first floor to the sixteenth floor.
Number of floors between first floor and fourth floor = 4 - 1 = 3,
and
number of floors between first floor and sixteenth floor = 16 - 1 = 15.
So, time taken by the elevator to travel 3 floors = 4 seconds.
Time taken by the elevator to travel 1 floor
Therefore, time taken by the elevator to travel 15 floors will be
Thus, the elevator takes 20 seconds to travel from first floor to sixteenth floor.