Correct Answer - A
`(1)/(F)=(1)/(f_l)+(1)/(f_m)+(1)/(f_l)`
`=(2)/(f_l)+(1)/(f_m)=2((3)/(2)-1)((1)/(infty)-(1)/(-30))+(1)/((30)/(2))`
`=(1)/(10)`
`F=10cm`
The silvered lens behaves as concave mirror of focal length 10 cm.
If object and image coincide, object should be placed at centre of curvature of mirror.
`u=2F=2xx10=20cm`.
![image](https://learnqa.s3.ap-south-1.amazonaws.com/images/161225152912808076161612251529.png)