A hard question that 90% can not answer

This is really a hard to answer question and 90% of high school graduates do not know the question.It is about the high power flashlight. A night watchman entered into an aquarium in the middle night because he heard the noise of flipping inside. A thief or an otter? He thought and threw light with his high power flashlight .

This high power flashlight generated a parallel beam from the end side of aquarium and illuminated a fish. Now what we know are as follows:

1)Angle of the beam with respect to the horizontal base of the aquarium is θ1 = 46.0                     2）the 1000 lumen flashlight  is 40 cm away from the glass window.                                           3) Glass thickness=10 cm                                                                                                                        4) The fish inside is 50 cm from the other side.                                                                                    5) Refractive index: nwater=1.33, nglass:1.52  nair:1.00                                                          Below is a drawing to show you.

Now, the question is:What is the distance y between the fish and the bottom of the aquarium and the real position of the fish?