Answer:
20 yards
Explanation:
The area of a square is calculated by multiplying its height by its base. Because they are the same in a square, the area of a square is obtained by squaring one of its sides. Let's call the sides 'x'. Then we can express the area of the garden as x^2=400.
From here we simply need to square root both sides which gives us:
x=20
Therefore the length of one side of the garden is 20 yards.
Hope this helped!