Which expression calculates the speed in meters per second of an object that travels a distance of 100 m every 20 s? 10020 100⋅20 100−20 100+20

The rule that relates between the speed, distance and time is as follows:
speed = distance / time

We are given that:
distance = 100 meters
time = 20 seconds

Substitute with the givens in the above equation to get the expression for the speed as follows:
speed = distance / time
speed = 100 / 20 meters / second

Hope this helps :)