## Conceptual Physics (12th Edition)

The Earth-moon distance is $3.8 \times 10^{8} m$, and the round-trip distance is twice that. If c denotes the speed of light, then $d = 7.6 \times 10^{8} m = ct$. Solve for t = d/c. $$\frac{7.6 \times 10^{8} m }{300,000,000 m/s} = 2.5 s$$