In this position-time graph or distance-time graph, there are three different part that shows three different velocities one in increasing as it moves from a lower position in relative to time and one is stationary and the third is decreasing.
'Straight lines' on a distance-time graph suggest that the movement of the object is constant. During 'Part B' of the journey the object travels 0m in 3s. It is stationary for 3 seconds so the velocity will be zero as well.
