Kinematics Question Help

Hello,
Could someone please explain why the time for the motorcycle is 42s.
I thought it would be 21 as I did 420/20.
(part iii of the question, i have attached the ms for reference.)

(edited 1 year ago)

It does not travel at a constant speed, rather it accelerates to 20m/s, and then decelerates to rest.

Sketch out the velocity/time graph of the motorcycle. The distance traveled is the area under the graph.
You want to figure out the time it takes to travel the distance. First of all, what shape does the velocity time graph take? Secondly, how would you express the area under the graph, and finally what quantities do you know? You can then rearrange for time.

Spoiler

(edited 1 year ago)