We are told that Tristan is planting a garden that's square shaped and its area is 64 square meters. Because 8 * 8 = 64, we have a square where each side is 8 meters along.
From an algebra point of view, where s is a side of the square,
s² = 64
s = 8 or s = -8 by taking square roots of both sides
s = 8 by discarding the -8 (lengths cannot be negative)
Now that we know a square's side we need its perimeter. Each side is the same, so a square's perimeter is four times a side.
4 * 8 = 32, which is our perimeter.
Therefore 32m² of material are needed.
