Use cylindrical coordinates to evaluate the triple integral \displaystyle \int \! \! \int \! \! \int_{\mathbf{e}} \, \sqrt{x^{2} + y^{2}} \, dv, where e is the solid bounded by the circular paraboloid z = 9 - 4 \left( x^{2} + y^{2} \right) and the xy -plane

The coverage of a base station of a telecommunication company forms a disk with a radius of (kilometers). let be the distance of a cellphone from a base station. assume that the location of cellphones in use are randomly uniformly distributed within the disk. calculate the mean and variance for the random variable.