A man rows his boat 90 km downstream and 72 km upstream, taking 3 hours each time. Find the speed of the stream?
Choose the correct choice
A) 6 B) 5 C) 7 D) 3 E) 2

Rationale: "speed downstream = d / t = 90 / 3 = 30 kmph speed upstream = d / t = 72 / ( 3 ) = 24 kmph the speed of the stream = ( 30 - 24 ) / 2 = 3 kmph answer : d"
Answer: D