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**solars** Water is flowing at a rate of 50 m^3/min into a holding tank shaped like a cone, sitting vertex down. THe tank's base radius is 20 m and has a height of 10m.

Write an expression for the rate of change of the water level with respect to time in terms of h(water's height in the tank).

I started off with the equation of V=(1/3)(pi)(r^2)(h) and implicitly differentiated that, but then I was wondering if I plug the 20 in for r first then differentiate, since I don't know dr/dt.