An object is placed 15 cm15 \, \text{cm}15cm in front of a plane mirror.

Initial Image Position: The image is 15 cm behind the mirror.

Mirror Movement: The mirror is moved 5 cm further away from the object, making the distance to the mirror 20 cm.

New Image Position: The new image is now also 20cm behind the mirror.

Conclusion

The total distance from the object to the image is 20 cm + 20 cm = 40 cm.