The answer is B, 12.56 mm. I found this by attempting to use the inverse operations on the formula for the surface area of a sphere. After dividing the S.A. by a quadrupled 3.14, I found 48.975159 and started to make guesses by multiplying the number by some of the multiple choice answers. The closest product from an answer was from 12.56, with a result rounding to 615. So all in all, I think its B.