The shift in position of object due to slab is given by
Δt=t(1−1μ)=3(1−132)=3(1−23)=1cm
The apparent distance of object from mirror 21−1=20cm
The position of image formed by concave mirror can be found by mirror formula
1v+1u=1f...(i)
As object and focus of mirror lies left side of pole of mirror
u=−20,f=−R2=−5
substituting values in equation (i)
1v+1−20=1−5
1v=120−420
v=−203
As image is other side of the slab,the image will be again shifted by 1 cm away from mirror.
Final distance of image from mirror=203+1cm=7.67cm