Find the surface area of a sphere with a circumference of 40 ft. round to the nearest tenth.

a) 6.4
b) 509.3
c) 245.6
d) 40.5

The circumference of the sphere is calculated through the equation, C = 2πr. Rearranging the equation gives an equation for r which is r = C/2π. Substituting, 
                                        r = 40 ft / 2π = 6.366 ft
The equation for the surface area of the sphere is SA = 4πr². Substituting the value of radius,
                                        SA = 4π x (6.366 ft)² = 509.30 ft²
Thus, the answer is letter B. 509.3 ft².