$${W_r = U_{180^{\circ}} - U_0 = (-pE \cos 180^{\circ}) - \\ (-pE \cos 0) = 2pE = (2)(6,2 \times 10^{-30}\, \mathrm{C \cdot m}) \\ (1,5 \times 10^4\, \mathrm{N/C}) = \underline{\underline{1,9 \times 10^{-25}\, \mathrm{J}}}}$$