Please explain in detail the problem and how it is needing t

Please explain in detail the problem and how it is needing to be solved. I want a step-by-step of how to do the problem so I can see where I am going wrong. To help, the answer from the answer key is:

Solution

Take a ring at a height x from the top and ring height dx, infinitesimally small F = PA on this ring is \\(\ ho g x \\times (2\\pi r dx)\\) Integrating this from 0 to h: \\(\ ho g 2\\pi r\\int_{0}^{h} x dx) = \ ho g \\pi d h^2/2 = 2\\pi (9.8) 900 N\\)