A boat can travel with a speed of 25km/hr in still water. If the speed of the stream is 5km/hr, find the time taken by the boat to go 120km downstream. Choose the correct answer.
A) 1 hr  B) 2 hrs  C) 3 hrs  D) 4 hrs  E) 5 hrs

Rationale: "speed downstream = ( 25 + 5 ) km / hr = 30 km / hr . time taken to travel 120 km downstream = 120 / 30 hrs = 4 hrs . answer : d"
Answer: D