Gauss practice (easy)

The earth has a net electric charge. The resulting electric field is, on average, $150~\mbox{V/m}$ and it is directed toward the center of the earth. What is the magnitude of the Earth's net charge in Coulombs ? You may assume that the charge is uniformly distributed over the Earth's surface and that the earth is a perfect sphere.

• $k=\frac{1}{4\pi \epsilon_{0}}=9\times 10^{9}~\mbox{Nm}^{2}/\mbox{C}^{2}$
• The radius of the earth is $6370~\mbox{km}$ .