Ramesh rows a boat in still water at a speed of 4.5 km/h to go and to come back. If the river flows at a speed of 1.5 km/h, then, his average speed for the whole journey is:

3 km/h 4.5 km/h 4 km/h 6 km/h

4 km/h

The correct answer is Option (3) → 4 km/h