oooooooooptics

I 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 ??

Ashish is right.

In the picture you can see that the distance OI is constant.

Now you got the hint ?

thanks bhaiya u rock!