Given that the image distance is v = -20cm
The object distance is u = -380 cm.
We have to find the focal length, f.
The formula to find the focal length is
[tex]\frac{1}{f}=\frac{1}{u}+\frac{1}{v}[/tex]Substituting the values, the focal length will be
[tex]\begin{gathered} \frac{1}{f}=\frac{1}{-380}+\frac{1}{-20} \\ =-\frac{1}{19} \\ f=-19\text{ cm} \end{gathered}[/tex]Thus, the focal length is -19 cm.
