Solomon six shooter fires a gun if the bullet leaves the barrel of the gun with velocity of 500 meters per second how long will it take to travel 2000 meters?

That's going to depend a lot on what direction he points the gun when he fires it.

For example, if he's holding it level and fires parallel to the ground, then
it would travel 2,000 meters in (2000/500) = 4 seconds after the shot. 
BUT . . . in order to accomplish that, the muzzle would have to be at least
78 meters (about 255 feet) up off the ground, because anything that's being
attracted by gravity falls about 255 feet in 4 seconds, and if the bullet hit the
ground sooner than that, then it would stop traveling horizontally.

If he points the gun straight up, then the bullet reaches 2,000 feet above
the muzzle in 4.17 seconds after the shot.  It keeps going up, tops out when
it runs out of speed, starts falling, and returns to 2,000 feet again at about
98 seconds after the shot.  (At 102 seconds after the shot, it is hoped that
Solomon has moved out of the way, because that's when the bullet returns
to the ground, at the same speed of 500 m/s that it had when it was fired
straight up.  That speed is a little over 1,100 mph, believe it or not, and that
little tiny piece of lead falling out of the sky is dangerous.  Solomon would
not be wise to stand there and look up.)

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.