In terms of diameter (d), the area (A) of a circle is given by the formula
A = (π/4)d²
You have d=20 yd, so the area of the circle is
A = (π/4)×(20 yd)² . . . . substitute the given information into the formula
A = 100π yd² . . . . . . . . do the arithmetic
A ≈ 314.16 yd²