Six Degrees of Separation - U.S. States

If you know how US interstate highways are numbered, it's easy to guess. The rules have exceptions, but in general multiples of 10 (in this case, I-90) go from coast to coast. They're also in numerical order, south to north. So, the opposite end of I-90 from Washington has to be in a northeastern state. Also, I-90 in Boston is somewhat infamous, due to the Big Dig mega-project a couple decades back.

A similar rule applies for north-south highways - hence I-5 runs the length of the west coast, and I-95 runs the length of the east coast.

I'm a Brit so what do I know? But I assume the question means what state became a member of the Union during the Civil War when it wasn't before. If I understand the little American History that I know there were many states that were part of the Union before the Civil War. Then some left to form the Confederacy and then presumably rejoined after they lost

If this is correct then there would be many states that would not qualify under this question as it appears that only two joined the Union DURING the Civil War. Some states never left after they joined. Other states were members of the Union before the Civil War then left at the beginning and rejoined at or after the end

And some states joined well after the Civil War (e.g.Alaska and Hawaii). I fail to see, therefore, how all but one state satisfy the question.

And then have a quiz on 6 degrees of separation between those quizzes.