A man rows his boat 85 km downstream and 45 km upstream, taking 2 1/2 hours each time. Find the speed of the stream?

A. 5 kmph
B. 6 kmph
C. 7 kmph
D. 8 kmph
Explanation:
Speed downstream = d/t = 85/(2 1/2) = 34 kmph
Speed upstream = d/t = 45/(2 1/2) = 18 kmph
The speed of the stream = (34 – 18)/2 = 8 kmph