To find how many bags you need you need to find the are of the circular field.
The area of a circle is:
[tex]A=\pi\cdot r^2[/tex]The area of the circular field is:
[tex]A=\pi\cdot(58ft)^2=10568.3ft^2[/tex]As 1 bag cover 355 square feet, you divide the area of the field into 355 to find how many bags you need:
[tex]\frac{10568.3ft^2}{355ft^2}=29.76[/tex]Then, you need at least 29.76 or approximately 30 bags