Remember, the diameter is . So if the diameter is doubled, then the new radius is units (instead of "r" units)
Start with the given equation.
Replace the original "r" with "2r".
Square 2r to get
So the old equation is and the new one is
The ratio of the new surface area to the old surface area is then:
Highlight the common terms
Cancel out the common terms
Simplify
So the new surface area is simply 4 times the original surface area. So the answer is B
