Answer:
B. Truck X had a head start, not truck Y.
Explanation:
Let's see what data can we obtain from this information.
Truck X's position changed from point (0,20) to point (2.8,50). That means that it started on the 20th kilometer and in the next 2.8 hours reached 50 km. It's velocity, then, is v1 = (s2 - s1) / t
v1 = (50 - 20) / 2.8
v1 = 10.7 km/h
Since it started from 20th km that means it had head start and since its line on the graph is straight, that means that its velocity was constant and that it didn't change direction.
Truck Y's position changed from the origin (0,0) to the point (5,20). That means it crossed 20 km in 5 hours, so its velocity is v2 = 20 / 5
v2 = 4 km/h
Again, since its line on the graph is straight, its velocity is constant and it did not change direction.
Now, knowing this, we can see that Rosa's mistake was to claim that truck Y had head start.