A walks at 10 kmph and 6 hours after his start, B cycles after him at 20 kmph. How far from the start does B catch up with A?
Choose the most appropriate option.
A) 100km  B) 150km  C) 50km  D) 120km  E) 200km
Suppose after x km from the start B catches up with A. Then, the difference in the time taken by A to cover x km and that taken by B to cover x km is 6 hours.   x/10 - x/20 = 6   x = 120 km   Answer is 120km
<result>D</result>
A walks at 10 kmph and 6 hours after his start, B cycles after him at 20 kmph. How far from the start does B catch up with A?