I think the logical question here is to either find the distance or the displacement. They differ in such a way that distance is a scalar quantity that does not focus on the direction. Displacement is a vector quantity that covers the distance from the starting point to end point. Because it travels only in one direction (to the east), in this condition, distance is equal to displacement.
Distance = Displacement = 3,000 m + 1,500 m = 4,500 m
Answer:
The angle between the emergent blue and red light is 
Explanation:
We have according to Snell's law

Since medium from which light enter's is air thus 
Thus for blue incident light we have

Similarly using the same procedure for red light we have

Thus the absolute value of angle between the refracted blue and red light is
