Volume of Solid: Frustum of Right Circular Cone

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Homework Statement


Find the volume of the solid S.

A frustum of a right circular cone with height h, lower base radius R, and top radius r.



Homework Equations


the integral of (pi)(r^2) [top] - (pi)(r^2) [bottom] dx


The Attempt at a Solution


I don't know how to start. I know I need to find the endpoints where the cross sections meet, but I'm not sure how to go about that.
 
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Divide the frustrum into circles of thickness dy. The area of the circle will be a function of y. Integrate to find the volume.
 
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