3. What should be the depth of the water in an octagonal tank 6 meters across flats in order to provide 12,500 gallons?

Solution:

The base is an octagonal, so the area of base

S(base) = 6*6 - 4*(27-18sqrt(2)) = 29.82 sq meters

1 gallon = 0.0038 cubic meters

12500 gallons = 47.32 cubic meters

The height = V/S = 47.32/29.82 = 1.59 meters

So the depth should be 1.59 meters