a container in the shape of an inverted triangular pyramid has a top in the shape of an equilateral triangle whose side length is 1 foot. the depth of the pyramid is also 1 foot. the pyramid is filled with sand at the start, and sand leaks at 0.2 ft3/min. how long does it take for the container to empty? how quickly is the level of the sand falling when the container is half way to being empty?