1I am giving you a hint dear.
If you see carefully the lens/mirror formula ( only for real images )
The distance between the image & the object doesnot change if you swap the u & v.
I mean if an object was at a distance x left of convex lens & image was formed y distance on right side of convex lens, then distance between object & image is x+y.
Now, switch u & v.... i mean if you now place the object at a distance y left of lens then image will form x distance right of the lens. so the distance between object & image is still the same ... x+y
Its the same case here ... did u get it ??
