Easy volumes question Note: I am trying to prepare, i already see the answer to this question but i dont understand it.
It says volume of earth used for making the embarkment = $\pi (R^2 - r^2)h$
But i dont understand, what R? What r?The whole part solves out to 28$\pi$ but i dont understand where the two Rr come from and what are their values
The question is: A well of diameter 3m is dug 14m deep. The earth taken out has been spread evenly all around it in the shape of a circular ring of width 4m. Find the height of the embarkment.
I think that width refers to the diameter but i am not sure about that either, would be really helpful if someone explained the answer to me properly, my guide book sure doesnt D:

The total volume of earth taken out is $r^2\pi\cdot h=3^2\pi\cdot14$. The volume of the new pile is $(R^2-r^2)\pi\cdot H=(4^2-3^2)\pi H$, where you need to find $H$. Compare the two, and express $H$.
