c) To determine the velocity of the motion at the given time, consider that the velocity is also the area under the line of the graph a vs t.
Between t=0s and t = 2 s, the area under the line is:
A1 = 2 X 2 = 4
Then, until t = 2s the velocity is 4 m/s
The area between t = 2s and t = 4 s is:
A2 = 2 x 0 = 0
The area between t = 4s and t = 5s, the area is:
A3 = 2 x 1 = 2
Now, consider that the velocity is the sum of the previous areas, but taking areas on the negative y-axis as negative ones. Then, you have:
A = A1 + A2 - A3 = 4 + 0 - 2 = 2
Hence, the velocity is 2 m/s