Use the interactive applet for visual understanding of speed time graphs.
This applet can model any given text problems of up to 5 distinct parts of a total journey. Updated 20 Sep 2017 to include option to better adjust the parts of journey.
Original version at https://www.geogebra.org/m/YpTfUB6Z
You can use the ShowViewScaleControls to modify the scale and views of the axes, and values.
The horizontal is in time units (you can set it to seconds, minutes or hours), and the vertical is
in units per time unit so you can set it to metres or kilometres per time unit (depending on your x axis units)

Some questions based on initial diagram of applet for your self discovery
1. Find the distance travelled (units) for the first 20 units of time.
2. Is the car turning back between E & F?
Some questions/situations for you to explore.
3. Alter the speed time graph such that the car after time at 20 units (at C) slows down uniformly to stop and rests (does not move)
for the period from D to E for 10 time units. It then moves with uniform acceleration for another 10 time units such that the total
journey distance is 600 units.