A man rows his boat 90 km downstream and 55 km upstream, taking 3 hours each time. Find the speed of the stream?
Choose the correct choice from the following answers:  A) 76 kmph  B) 6 kmph  C) 14 kmph  D) 8 kmph  E) 4 kmph

Rationale: "speed downstream = d / t = 90 / ( 3 ) = 30 kmph speed upstream = d / t = 55 / ( 3 ) = 18 kmph the speed of the stream = ( 30 - 18 ) / 2 = 6 kmph answer : b"
Answer: B