To find the radius of the original circle before applying the scale factor, you can use the formula:
\[ \text{Original Radius} = \frac{\text{Dilated Radius}}{\text{Scale Factor}} \]
Given that the dilated radius is 18 cm and the scale factor is 15:
\[ \text{Original Radius} = \frac{18 \text{ cm}}{15} = 1.2 \text{ cm} \]
It seems that the options provided do not include this value. Therefore, there may be some confusion with the question or the options presented. Based on the calculations, the original radius should be 1.2 cm. If you meant something else, please clarify!