A walks at 10 kmph and 3 hours after his start, B cycles after him at 20 kmph. How far from the start does B catch up with A?
Choose the correct choice from the following:
A) 100 km
B) 150 km
C) 60 km
D) 120 km
E) 200 km

Rationale: "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 3 hours . x / 10 - x / 20 = 3 x = 60 km answer is c"
Answer: C