Three thin, concentric, conducting spherical shells have radii \(R\), \(2R\), and \(3R\). The innermost shell carries a net charge \(+Q\), the outermost shell carries a net charge \(-Q\), and the middle shell is connected to ground so that its electric potential is zero. Expressed in terms of Coulomb's constant \(k = \dfrac{1}{4\pi\varepsilon_0}\), \(Q\), and \(R\), what is the total electrostatic potential energy stored in this system?