<PRE><B>Question 253161</B>

1 . Forget the airport. Planes are moving apart at 840 + 860 = 1700 kph
Time when 6800 apart is 6800/1700 = 4 hours
2. 1st man  does 5.6 kph, second man does 6 kph, total closing velocity is 11.6 kph. After 1.5 hours they are 1.5 x 11.6 = 17.4 km closer that at the start
3. after 12 minutes, a has a lead of 12/5 = 2.4 km (12 minutes = 1/5 of hour)
difference in velocity between A and B is 6 kph, so how long does it take to cover 2.4 km at 6 kph. (2.4 / 6) = 2.5 hour or 24 minutes.
4. The time he leaves is irrelevant. 
Distance = 60T = 80 (T - 3/2)
60T = 80T - 120
so T = 6
Total time is therefore 6 + 4.5 = 10.5 hours

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