If you know that a person is running 100 feet every 1 seconds, you can determine their velocity. Velocity is the rate of motion. i.e. the rate at which the person is running. Velocity is given by distance / time. In the given question the distance is 100 feet while the time is 12 seconds. So to determine the velocity, we divide 100 by 12 to get 8.33 feet per second.
