A man swims downstream 30 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?

A. 2 kmph
B. 8 kmph
C. 16 kmph
D. 4 kmph
Explanation:
30 — 3 DS = 10
? —- 1
18 —- 3 US = 6
? —- 1 M = ?
M = (10 + 6)/2 = 8