Task: Question Answering
Input (English): Problem: a , b , k start from the same place and travel in the same direction at speeds of 30 km / hr , 40 km / hr , 80 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 ? 
Options: a ) 2 , b ) 3 , c ) 4 , d ) 5 , e ) 6
Output (English): d