Problem: the surface area of a sphere is 4 π r ^ 2 , where r is the radius of the sphere . if the surface area of sphere a is eight times as large as the surface area of sphere b , then the radius of sphere a is how many times the radius of sphere b ? 
Options: ['a ) 2', 'b ) 2 √ 2', 'c ) 4', 'd ) 2 π', 'e ) π · √ 8']
b