How long does light take?

Light is the fastest thing there is, yet it still takes time to cross space. You will make the program find how long light takes for several trips, and then show each time with the most sensible prefix, from nanoseconds to seconds.

The idea. $t = \dfrac{d}{c}$, with $c = 3.0 \times 10^{8}\ \text{m/s}$. A good prefix keeps the number between $1$ and $1000$: $67\ \text{ns}$ reads better than $6.7 \times 10^{-8}\ \text{s}$.

Your tasks.

1. Work out the time for each trip, in seconds.
2. Make nice(t) choose the largest unit that is not bigger than t, and write the time in it.
3. Find how many times longer the Mars trip is than the Moon trip.