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## Homework Statement

A large container has the shape of a frustum of a cone with top radius 9 metres , bottom radius 2 metres , and height 7 metres. The container is being filled with water at the constant rate of 4.2 cubic meters per minute.

At what rate is the level of water rising at the instant the water is 1 metre deep?

## Homework Equations

V = 1/3∏ (r^2) * h

Internet Says the volume of a frustum of a cone is V = (∏ * h / 3) (R^2 + Rr + r^2)

## The Attempt at a Solution

I don't know where to start with this one, I think I have to find some relationship between the height of the cone and the radius of the cone, however, I don't know which radius to use. Once I isolate h with V, I can just derive it and substitute 4.2 for dV/dt, 1 for h, and find dh/dt. Any tips on how to relate radius to height in this situation? Thanks in advance.