A ruptured oil tanker causes a circular oil slick on the surface of the ocean. When its radius is 150 meters, the radius of the slick is expanding by 0.1 meter/minute and its thickness is 0.02 meter. At that moment:

(a) How fast is the area of the slick expanding?

(b) The circular slick has the same thickness everywhere, and the volume of oil spilled remains fixed. How fast is the thickness of the slick decreasing?

(a) For this one, I'm not sure whether by "area" they mean surface area (since I think we'd be dealing with a cylinder), or just an area of the top circle (the top of the cylinder)?

(b) I'll come back and work this one if you guys help me with the first one.