Abullet is fired horizontally from the top of a building with a muzzle velocity of 150 m/s. a similar bullet dropped from the top of the same building, takes 4 sec to reach the ground. how far forward does the first bullet go before it hits the ground?

The bullet dropped takes 4 seconds so you can calculate the height by using the formula
s = ut + 1/2 at^2
her u = 0
s = 1/2 * 10 * 16 = 80 m
similarly if the bullet is porjected horizontally also it will take 4 seconds to reach the ground.
Remember that there is no acceleration in horizontal direction.
so
distance travelled in horizontal direction = time * initial component = 4 * 150 =600 meters
There you have your answer. Hope it helps