Hello!
Here we have a distance wanted with givens of constant speed and total time. The equation to find distance with a constant speed is d=v*t where, v=2.5m/s t=20s therefore we have:
d=2.5m/s * 20s = 50m traveled
We can think about this situation with constant speed of units m/s meaning every second they travel x amount of meters and x being 2.5 in this problem. Then, if we know they go 2.5m every second, and we know they travel for 20s, then we can intuitively see it will be the total distance covered per sec times or multiplied by the total number of seconds for total distance traveled.
Also, we can see that the units are m/s so to get meters alone which is a unit of distance, we can see that we need to multiply by seconds to cancel the seconds on the bottom in the units and only be left with meters on top for our final units.
Hope this helps you understands the concept better. If you have any questions at all, please just ask! Thanks so much!! Keep up the hard work!!