A thin, nonconducting spherical shell of radius \(R\) carries a total positive charge \(Q\) distributed uniformly over its surface. The shell is allowed to expand radially outward under its own electrostatic repulsion until its radius becomes \(2R\), while its total charge remains constant. Which of the following correctly pairs the work done by the electrostatic forces during the expansion, \(W_{\text{field}}\), with the final electrostatic potential energy of the system, \(U_f\)?