Answer: 30 seconds.
Step-by-step explanation:
A person on a moving sidewalk travels 36 feet in 9 seconds. This means that for 1 second, the person travels for 36/9 = 4 feet.
Since the moving sidewalk has a length of 120 feet, the time taken to travel from one end to another will be:
= 120 / 4
= 30 seconds