Answer a galactic math problem for me?

Say that a long time ago, in a galaxy far, far away, two planets collided . . .

If the event occurred 3 billion years ago, and a hunk of debris the size of a refrigerator entered Earth’s atmosphere today, how many light years away did the collision take place?

I know that gravity and probability dictate that this hunk never makes to Earth but let’s just say it did. I’m looking for a rough distance here.

Thanks.