The area of a circle is given by the following expression:

Where A is the area and r is the radius of the circle.
According to the picture, the diameter of the circle is given. We can find the radius by dividing the diameter by 2, this way:

The radius of the circle is 6 in.
Use this value and the expression given to find the area of the circle, this way:

Replacing r by 6 we obtain that the area of the circle is 113.09 in^2.