Answer
$5.71\times10^{13}C$.
Work Step by Step
The electrical force equals the gravitational attraction.
$$F_E=F_G$$
$$k\frac{Q^2}{r^2}=G\frac{M_EM_m}{r^2}$$
$$Q=\sqrt{ G\frac{M_EM_m}{k}}$$
Use the data from the inside front cover of the book.
$$Q=\sqrt{6.67\times10^{-11}\frac{(5.98\times10^{24}kg)(7.35\times10^{22}kg) }{8.988\times10^{9}}}=5.71\times10^{13}C$$