Radius of curvature of converging mirror(concave mirror) is $30\ \text{cm}$. To obtain a virtual image in case of concave mirror, object should be placed between pole and focus. Using, Focal length:$\frac{\;\text{ Radius }\;}{2}=\;\frac{30}{2}=15\ \text{cm}$Therefore, object should be placed between 0 $\text{cm}$ and $15\ \text{cm}$.