The radius of the sphere is 6 millimeters. Which equation can be used to find the surface area of the sphere? A sphere with a radius of 6 millimeters. S = 4 pi r squared = 4 (6) squared S = 4 pi r squared = 4 pi (12) squared S = 4 pi r squared = 4 pi (6) squared + 2 pi (6) S = 4 pi r squared = 4 pi (6) squared