Two boys starts from the same place walking at the rate of 4 kmph and 5.5 kmph respectively in the same direction. What time will they take to be 10.5 km apart?
Choose the correct option
A) 8	B) 5	C) 7	D) 9	E) 6

Rationale: "explanation : relative speed = 5.5 - 4 = 1.5 kmph ( because they walk in the same direction ) distance = 10.5 km time = distance / speed = 10.5 / 1.5 = 7 hr answer : c"
Answer: C