Hello
1) The total distance the light has to cover to go from Earth to the Moon and back is twice the distance between the Earth and the Moon:
[tex]S=2d=2\cdot 3.8 \cdot 10^8~m =7.6 \cdot 10^8~m[/tex]
2) Given the relationship
[tex]v= \frac{S}{t} [/tex]
where [tex]v=3\cdot10^8~m/s[/tex] is the speed of light, S the total distance covered calculate at point 1), and t the time, we can find the time the light needs to go from Earth to the Moon and back again:
[tex]t= \frac{S}{v}= \frac{7.6\cdot10^8 m}{3\cdot10^8~m/s}=2.53~s [/tex]
