Let, speed of ferry = u km/h
and speed of still water = v km/h
downstream speed, u + v = 45 km/hr
upstream speed, u – v = 30 km/hr
∴ u = 37.5 km/h and v = 7.5 km/h
Again, let speed of passenger in the river is x km/h.
From question,
+==x−7.5=9x=16.5km/h
Hence, speed of passenger in the river = 16.5 km/h. None of the given options matched