The mass of earth is $6.00 \times 10^{24} \;kg$ and that of the moon is $7.40 \times 10 ^{22} \;kg \;$ and $G= 6.67 \times 10^{-11} Nm^2 /kg^2$. potential energy of the system is $-7.79 \times 10^{28} J$. The mean distance of between earth and moon is

Question

$$(a)\;3.80 \times 10^8 \;m \quad (b)\;3.37 \times 10^6 \;m \quad (c)\;2.60 \times 10^4\; m \quad (d)\;1.90 \times 10^2 \;m$$