A cannot be the answer.
The maximum distance he can travel is 420 miles. He has gone 180. He still has 420 - 180 = 240 miles left to go.
C The distance is correct in the first set of brackets, but you cannot add distance divided by time (which is a speed) to distance.
D is incorrect. The first set of brackets is correct, but the second set is meaningless. Distances and rates do not mix.
B <<<<< Answer If you divide the remaining distance (240) by the rate (180/3) you get the correct answer of 4 hours.
B <<<< answer.
