Use the formula for the area of a circle and solve for the radius. (rounding to the nearest whole number)
\(A_O= \pi r^2 \\ 78.57 = 3.14r^2 \\ 25 = r^2 \\ \boxed{5 = r}\)
And of course, if the radius of a circle is 5 meters, then the diameter is 10 meters.
