You are standing on a fish pond wishing to catch a fish. How would you aim your fish gun in order to catch a fish which your eyes could see 20 cm below the surface of water ? will u aim higher , lower or exactly on the location of the fish as seen by your eyes ?

Question

You are standing on a fish pond wishing to catch a fish. How would you aim your fish gun in order to catch a fish which your eyes could see 20 cm below the surface of water ? will u aim higher , lower or exactly on  the location of the fish as seen by your eyes ?

find out what determines how large the bending of the light ray is when it  through a different medium ? 
 i have no idea how to do this because our teacher didn't teach this . please give me the idea or teach e how please please thank u very much