How much water ( level from bottom in cm )should be filled in a container 21 cm in height, so that it appears half filled when viewed from the top of the container  (given that  aμω=43)

To see the container half-filled from top, water should be filled up to height x so that bottom of the container should appear to be raised upto height (21–x). As shown in figure apparent depth h=(21−x)Real depth  h = x∴μ=hh′⇒43=x21−x⇒x=12cm