An inverted conical water tank with a height of [math] meters and a radius of [math] meters is drained through a hole in the vertex at a rate of [math] meters cubed per second. What is the rate of change of the water depth when the water depth is [math] meters?
Remember: The volume of a cone is [math].

[math]
You can enter in [math] as "pi".

(you will lose 25% of your points if you do)