The Radius of a Spherical Balloon Increases at a Rate $\mathrm { r } ^ { 2 }$

Short Answer

The radius of a spherical balloon increases at a rate of 1 mm/sec. How fast is the surface area increasing when the radius is 10mm? (Note: The surface area S of a sphere of radius r is S = 4π $\mathrm { r } ^ { 2 }$ .) Enter just a real number (no approximations, no units or words).