A spherical balloon is inflating with helium at a rate of 128 ft³/min. How fast is the balloon's radius increasing at the instant the radius is 4 ft? How fast is the surface area increasing? The balloon's radius is increasing at a rate of (Simplify your answer.) ft/minat the instant the radius is 4ft. The surface area is increasing at a rate of ☐ ft²/min at the instant the radius is 4 ft. (Type an exact answer, using as needed.)