Answer:
The given equation is

Which is the definition of the angle of repose.
<em>Remember that the angle of repose refers to the angle between the horizontal plane and the inclined side of the cone formed when we allow to fall freely granular materials.</em>
We know by given

Replacing these values, we have

Therefore, the angle of repose is 38.29° approximately.
Now, if the base diameter is 104 feet, the height would be

Therefore, the height would be 65.8 feet, assuming that the angle of repose is the same.