Afish can travel 30km/h in still water. how long will it take to arrive 12km downstream in a river flowing 6km/h?

30 + 6 = 36

36/12 = 3

So, it would take it 3 hours to go 12 kms downstream.

Note that we added 30 and 6 because it was going downstream. If it was going upstream, then we would have had to subtract.

Neptune is the eighth planet from the sun. it was the first planet to get its existence predicted by  mathematical calculations  before it was actually seen through a telescope on sept. 23, 1846. irregularities in the orbit of  uranus  led french astronomer alexis bouvard to suggest that the gravitational pull from another celestial body might be responsible. german astronomer johann galle then relied on subsequent calculations to   spot neptune via telescope. previously, astronomer galileo galilei sketched the planet, but he mistook it for a star due to its slow motion. in accordance with all the other planets seen in the sky, this new world was given a name from greek and roman mythology — neptune, the roman god of the sea.