Hello Mr RayonSuppose Samuel can row at km/h in still water. Then his speed when he's rowing with the current is km/h, and km/h when he's rowing against the current.

So if we now use the formuladistance = speedxtime, we can find the distance he rows in each direction, and then say they are the same.

1 h 20 min = h = h. So on the way out he rows km. And on the way back he rows km.

So

So he rows at 4 km/h in still water.

Grandad