A, B, K start from the same place and travel in the same direction at speeds of 30 km/hr, 40 km/hr, 100 km/hr respectively. B starts two hours after A. If B and K overtake A at the same instant, how many hours after A did K start?  Choose the correct option:
A) 4.2
B) 4.8
C) 5.6
D) 6.4
E) 7.2
In 2 hours, A travels 60 km.   B can catch A at a rate of 10 km/hr, so B catches A 6 hours after B starts.   So A and B both travel a distance of 240 km.   C needs 2.4 hours to travel 240 km, so C leaves 5.6 hours after A.   The answer is 5.6.
<result>C</result>
A, B, K start from the same place and travel in the same direction at speeds of 30 km/hr, 40 km/hr, 100 km/hr respectively. B starts two hours after A. If B and K overtake A at the same instant, how many hours after A did K start?