This question can be solved quickly using relative speed. The relative speed of the bus B(second bus) wrt A is 50-45= 5 mph(as both travel in the same direction)
The distance between them is 45 miles as the first bus covers that much in an hour while the second bus was stationary.
Hence the time taken by the second bus to bridge this gap is given by {total distance to be covered/relative speed}
Therefore 45/5=9 hrs. So in 9hrs both busses will meet and post that B crosses A.
Quantity A is greater and hence Option A is the answer.