Greetings!
To find speed with distance and time, you need to remember the speed formula:
Speed = distance ÷ time
So we need speed and we have the other two values, we can plug the values in:
Speed = 20 ÷ 2 = 10
The measurement for speed in this case is m/s (metres per second)
So the answer is 10m/s
Hope this helps!