In class problem
I am having trouble understanding #4e from todays worksheet: "Let $D$ denote the set in $\mathbb{R^3}$ lying above the cone $z=\sqrt{x^2+y^2}$ and below the plane $z=4$. Set up the following integrals over $D$ as iterated integrals in cylindrical coordinates. You should think about which ones you can evaluate. (e) An integral representing the volume of $D$."
What is the significance of setting up an integral representing the volume of $D$?