Recall that the speed at which an object travels is equal to the distance covered divided by the travel time, so the time elapsed is equal to the distance divided by the speed of travel.

The nebula's rate of expansion is 32 kilometers per second, so we need only to define a distance traveled (in kilometers) to calculate the travel time (in seconds).

Convert the distance covered from units of A.U. to units of kilometers, where each A.U. is equal to 1.5 × 10 kilometers.

We now have a length of time, in units of seconds. We can convert this to years, remembering that there are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day.