A walks at 10 kmph and 7 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 option
A) 100 km	B) 140 km	C) 50 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 7 hours . x / 10 - x / 20 = 7 x = 140 km answer is b"
Answer: B