The answer is: The surface area of the sphere.
The explanations for this exercise is shown below:
By definition, the surface area of a sphere is four times the area of a circle.
You have that the area of a circle is:
[tex] A=\pi r^{2} [/tex]
Where [tex] r [/tex] is the radius of the circle.
Therefore, to calculate the surface area of a sphere with radius [tex] r [/tex], you only need to multiply the equation shown above by four, as following:
[tex] SA=4\pi r^{2}
[/tex]
