a bullet is fired in a horizontal direction with a muzzles velocity of 300m/s

So what?

I suppose I could tell you when it hit ground and where if I knew how high the rifle was.
vertical problem:
v = - g t = -9.81 t
h = Hi - (1/2) g t^2
h = 0 at ground
so
4.9 t^2 = Hi the initial height, hits ground at t
then Horizontal problem, constant speed =300 m/s
x = 300 t = range