A man rows his boat 120 km downstream and 60 km upstream, taking 2 hours each time. Find the speed of the stream?
Choose one.
A) 6	B) 15	C) 17	D) 18	E) 2

Rationale: "speed downstream = d / t = 120 / ( 2 ) = 60 kmph speed upstream = d / t = 60 / ( 2 ) = 30 kmph the speed of the stream = ( 60 - 30 ) / 2 = 15 kmph answer : b"
Answer: B