50 points and ! quick

3. at a zoo, the lion pen has a ring-shaped sidewalk around it. the outer edge of the sidewalk is a circle with a radius of 11 m. the inner edge of the sidewalk is a circle with a radius of 9 m.

(a) write and simplify an expression for the exact area of the sidewalk.
(b) find the approximate area of the sidewalk. use 3.14 to approximate π.