-- Each square meter of the bottom of the tank has 4 cubic meters
of water standing on it.
-- 4 cubic meters of water is equivalent to 4,000 liters.
-- So its mass is roughly 4,000 kilograms, and its weight is roughly
(4,000 x 9.81) = 39,240 newtons.
-- So the pressure on the bottom is roughly 39,240 newtons per
square meter, or 39,240 pascals, or 39.24 kPa.