To find the area of a circle, you can use the formula:
\[ \text{Area} = \pi r^2 \]
where \( r \) is the radius of the circle.
In your equation \( C = 12x \), the \( C \) represents the circumference of the circle, which is given by the formula:
\[ C = 2\pi r \]
Setting these equal gives:
\[ 2\pi r = 12x \]
To find the radius \( r \), we can solve for \( r \):
\[ r = \frac{12x}{2\pi} = \frac{6x}{\pi} \]
Now we can substitute \( r \) back into the area formula:
\[ \text{Area} = \pi \left(\frac{6x}{\pi}\right)^2 \]
Calculating this gives:
\[ \text{Area} = \pi \cdot \frac{36x^2}{\pi^2} = \frac{36x^2}{\pi} \]
This result does not match any of the choices given (12x, 144x, 24x, 36x). It seems there might be a misunderstanding in the context of the problem since the choices provided do not represent the area of a circle based on the input data.
If you meant something different or have a specific question regarding \( C \) and \( x \), please clarify!