The speed of a boat in still water is 20 km/hr and the rate of current is 5 km/hr. The distance travelled downstream in 18 minutes is:	Pick one.
A) 9.5	B) 5.5	C) 7.5	D) 6.5	E) 5.1

Rationale: "explanation : speed downstream = ( 20 + 5 ) kmph = 25 kmph distance travelled = ( 25 * ( 18 / 60 ) ) km = 7.5 km . answer : c"
Answer: C