The perimeter of a square is four times the side, since you have to sum all sides, and they're all the same length:
[tex]P=n+n+n+n=4n[/tex]
This is direct variation, because we have
[tex]P=4n \iff \dfrac{P}{n}=4[/tex]
and if the ratio between two variables is constant (in this case, 4), then the two variables are in direct variation.
