31. A cylindrical tank with an open top has a diameter of 3mand
is completely filled with water. When the setting sun reachesan
angle of 28 degrees above the horizon, sunlight ceases
toilluminate the bottom of the tank. How deep is the tank? Hint:
When the sun is 28 degrees from the horizon, incidentrays are 62
degrees from the normal at the air-waterinterface.  Want an
answer?