Answer:
Step-by-step explanation:
If you go from 60 km/hr or 60 mph and apply your brakes so that you go down to 20 mph or 20 km/hr that is a decrease in velocity. It means you have to slow down because your are in a school zone or a neighborhood zone.
Deceleration can be defined this way.
d = (vf - vi) / t
where vi is bigger than your final velocity. In this case you are slowing down.