'n' = and blowin' = blowing in the wind (being blown about in the wind, can be found in the wind) (I think the song writer is saying that the answer is out there being blown around by the wind but you have to go find it yourself.)

"The answer is blowing in the wind." means that the answer is hard to find... just like something that is hard to grab / catch when it is being blown around by the wind. In my opinion, this idiom fits in well with the other lines as it calls up imagery of landscapes and weather just like the other two do (roads in the first line and seas in the second line). :)

* Why HAS this symbol BEEN used here? <--- Note that the subject comes between "has" and "been".