Work Step by Step
The velocity of any particular part of the graph can be found by finding the slope of the graph by finding the rise-over-run. for the first second, the graph increases by 10m in 1 second, resulting in $10m/s$ velocity. The graph is flat for the seconds and third seconds, so the velocity is $0$ for this time period. For the 4th second, the graph has the same slope and velocity as the first second. $20m-10m= 10m$ and $4s-3s=1s$ which is used to find $10m/s$.