Our nearest galactic neighbor, Andromeda, is ~3 million light-years away. Keeping in mind the definition of a light-year, how long in seconds does it take light from Andromeda to reach Earth?

9.4608 * 10¹³ seconds.

Explanation:

Data provided:

Distance of Andromeda from Earth = 3 million light years

Now,

3 million light year means that the light will take 3 million years to reach the Earth

also,

in 1 year there are (365 * 24 * 60 * 60) = 31536000 seconds

therefore,

3 million years in seconds = 3 million * 31536000 seconds

= 3,000,000 * 31536000

= 9.4608 * 10¹³ seconds.