If two students starting from same point, walking in the opposite directions with 6km/hr and 9km/hr as average speeds respectively. Then the distance between them after 4 hours is?  Choose the correct choice from the following options
A) 65 km
B) 55 km
C) 15 km
D) 60 km
E) 75 km

Rationale: explanation : total distance = distance traveled by person a + distance traveled by person b = ( 6 × 4 ) + ( 9 × 4 ) = 24 + 36 = 60 km answer : d
Answer: D