Answer
$A$ = 9 mi$^{2}$
$P$ = 12 mi
Work Step by Step
Since the length and width of the preserve are the same it is a square.
Area of a square: $A$ = $s$$^{2}$
$A$ = (3 mi) $^{2}$
$A$ = 9 mi$^{2}$
Perimeter of a square: $P$ = 4$s$
$P$ = 4(3 mi)
$P$ = 12 mi