To find the radius of the original circle before dilation, you can use the formula:
\[ \text{New radius} = \text{Scale factor} \times \text{Original radius} \]
In this case, you're given the new radius (18 cm) and the scale factor (15). Thus, you can rearrange the formula to find the original radius:
\[ \text{Original radius} = \frac{\text{New radius}}{\text{Scale factor}} = \frac{18 \text{ cm}}{15} \]
Calculating this:
\[ \text{Original radius} = \frac{18}{15} = 1.2 \text{ cm} \]
It appears that there might be an error in the choices you've provided, as 1.2 cm is not listed. If following this calculation with respect to the options you provided, please double-check the scale factor or the answers listed. If you meant a different problem altogether or different circle sizes, let me know!