An inverted conical water tank with a height of 14 ft and a radius of 7 ft is drained through a hole in the vertex at a rate of 8 f / (see figure). What is the rate of change of the water depth when the water depth is 4 ft? (Hint: Use similar triangles.) When the water depth is 4 ft, the rate of change of the water depth is about (Round to the nearest hundredth as needed.)