Given
The focal length is f= -20 cm
The image distance is v= -12cm
To find
The object distance
Explanation
The mirror formula is
[tex]\begin{gathered} \frac{1}{f}=\frac{1}{u}+\frac{1}{v} \\ \Rightarrow\frac{1}{^-20}=\frac{1}{u}+\frac{1}{^-12} \\ \Rightarrow u=30cm=3.0\times10\text{ cm} \end{gathered}[/tex]Conclusion
The object distance is 30x10 cm.
