The Van's speed is constant from 0 to 10 seconds, from 40 to 50, from 50 to 60, and from 60 to 70 seconds, although it has different valued in each interval. The speed is zero from 0 to 10 and from 50 to 60 seconds.
It may also be constant between 10 and 40 seconds. It's hard to tell ... someone has scratched all over the graph.
On a position/time graph, any STRAIGHT line represents constant speed.
