To solve for surface area of a sphere, the formula is 4*pi*r^2 where "r" is the radius. Since we know the diameter and that it is the length across the sphere, and that the radius is the distance from the center to the edge, we can divide the diameter by 2 to get the radius. This shows the radius is 5. Now all we have to do is substitute in the 5 for the "r" and solve.
SA=4*pi*r^2
SA=4*pi*5^2
SA=314.159
We are rounding to the hundredth here, so we can say the surface area of the sphere is (A) approximately 314.16 square miles.