A thin "layer" at height z will have surface area [itex]2\pi a dz[/itex]. Integrate that from 0 to h. No, you do not need that equation (which is not true anyway).
I find this very peculiar. You have posted a number of fairly standard Calculus problems but protested that you have no idea how to even begin? Are you not taking a Calculus course? Do you not have a calculus textbook?