Given the Central Angle:

And the diameter:
![d=18\operatorname{cm}]()
You need to use the following formula for calculating the area of a sector of the circle:

Where "r" is the radius of the circle and θ is the Central Angle (in degrees).
By definition, the radius is half the diameter. Then:
![r=\frac{18\operatorname{cm}}{2}=9cm]()
Then, substituting values into the formula and evaluating, you get:

![A=45\pi\text{ }\operatorname{cm}^2]()
Hence, the answer is:
![A=45\pi\text{ }\operatorname{cm}^2]()