Let's calculate the total charge of [tex]N=6.0 \cdot 10^{13}[/tex] electrons. Each electron has a charge of [tex]e=-1.6 \cdot 10^{-19}C[/tex], so the total charge is
[tex]Q_e=Ne=(6.0 \cdot 10^{13})(-1.6 \cdot 10^{-19}C)=-9.6 \cdot 10^{-6}C[/tex]
The initial charge of the sphere was
[tex]Q_i = +8.0 mC=8.0 \cdot 10^{-3}C[/tex]
Therefore, the final net charge will be
[tex]Q_f = Q_i + Q_e = 8.0\cdot 10^{-3}C-9.6 \cdot 10^{-6}C=+7.99 \cdot 10^{-3}C[/tex]
