\(W\,\, = \,\, - \Delta PE\,\, = \,\,\frac{{{q_1}{q_2}}}{{4\pi \,\,{ \in _0}}}\,\,\left[ {\frac{1}{{{r_f}}}\,\, - \,\,\frac{1}{{{r_i}}}} \right]\,\,\, = \,\,10\,\, \times \,\,2\,\, \times \,\,{10^{ - 12}}\, \times \,\,9\,\, \times \,\,{10^9}\,\,\left[ {\frac{1}{{0.6}}\,\, - \,\,\frac{1}{{0.8}}} \right]\,\, = \,\,0.075\,\,J\)