Answer:
A circle is a bounded object with points from its center to its circumference is equidistant.
Area of a circle = πr²
Where :
π = pi = 3.14
R = radius = diameter / 2 = 20m / 2 = 10m
3.14 x 10² = 314m²
Number of boxes needed to cover the garden = area of the garden / coverage of one box
314m² / 58m² = 5.14
5 boxes to one significant figure