At t 1 the speed is slow. At t 2 the speed is fast. At t 3 the speed is zero. At t 4 there is reverse speed. With constant speed, the position increases linearly with time.
Blue areas become red lines.
Each of the small blue areas gives a position change of 30km. The total blue area gives a position change of 120km. An object changes its position as shown. Find the speed between 0s and 1s, and also at 3s. Find the position of the object at 5s.