Diameter of 9cm means a radius of 4.5cm, concentric with a circle of radius 8cm. The question doesn't ask for anything, so assume that it's the area of the "washer", that is, the area between the inner and outer circles that's needed. This area is (pi)8^2-(pi)4.5^2=(pi)(8^2-4.5^2)=(pi)(8-4.5)(8+4.5)=(pi)(3.5*12.5)=43.75(pi)=137.44cc approx.
The general formula is Area=(pi)(R^2-r^2) or (pi)(R-r)(R+r) where R is the larger radius and r is the smaller radius.
The circles don't need to be concentric as long as the inner circle is completely within the outer circle.