To solve this problem it is necessary to apply the kinematic equations of description of the movement in which it is understood that the velocity is the travel of a particle in a fraction of time, that is to say
[tex]v = \frac{x}{t}[/tex]
Where,
x = Displacement
t = time
In our case the speed is equivalent to that of the Light, and the distance is necessary to reach the moon by the asteroid.
[tex]v = 3.8*10^8m/s[/tex]
[tex]x = 3.84*10^5km = 3.84*10^8m[/tex]
Re-arrange to find t,
[tex]t = \frac{x}{V}[/tex]
[tex]t = \frac{3.84*10^8}{3.8*10^8}[/tex]
[tex]t = 1.28s[/tex]
Therefore will take 1.28 s for the light arrive on Earth.