$${\begin{align}U_0 &= -\frac{GMm}{R} \\& = \mathrm{\frac{(6,67 \times 10^{-11}\, N \cdot m^2/kg^2)(5,89 \times 10^{24}\, kg)(7,20\, kg)}{(2)(6,37 \times 10^6\, m)}} \\&= -4,51 \times 10^{8}\, \mathrm{J} = \underline{-451\, \mathrm{MJ}}\end{align}}$$