1u just think of the case that... as to where the object is to be such that the image is formed there itself..... it is at the center of curvature..... i.e. at a distance of R from the pole......
therefore...
the height above the surface of water where the image is observable is μx ...where x is the distance above the surface where the object is to be placed...
So, μx + h = R
implies x = R - hμ