Two point charges with charge magnitudes \(+q\) and \(+3q\) are fixed a distance \(d\) apart. The electric potential energy of this two-charge system is \(U_0\). The charge \(+q\) is then replaced by a charge \(+2q\), and the distance between the two charges is reduced to \(\dfrac{d}{2}\). What is the new electric potential energy of the system in terms of \(U_0\)?