Acceleration- Time- Diagram

Below you can see an acceleration- time diagram. A car drives with a constant acceleration of a(t) = 5 m/s² . With the blue slider a you can change this constant acceleration. The velocity (m/s) of the car is calculated as the area under the linear function a(t). Through changing point B the calculated area under the linear function can be changed depending on time (seconds).
Tasks: a) Keep the time constant at 4 seconds (B=(4,0)) and change the acceleration through changing the slider bar a. What happens at a 1) higher 2) lower acceleration? b) Keep the acceleration constant and write down the velocity of the car after 2, 4, 6, 8, 10, 15 and 20 seconds. How does the velocity change with time? Try to find the function: v(t) = ............................................