After looking around, I really can't find any chart. But you told me the distance covered and the time it takes to cover the distance, so I can calculate the speed by using a pretty simple formula ... it's actually the definition of speed, and it'll be useful to you if you memorize it:
Speed = (distance covered) divided by (time to cover the distance) .
With the numbers you gave in your question ...
Speed = (400 meters) / (20 seconds)
Speed = 20 meters/second