A charged cloud system produces an electric field in the air near Earth's surface. A particle of charge $-2.0 \times 10^{-9} \mathrm{C}$ is acted on by a downward electrostatic force of $3.0 \times 10^{-6} \mathrm{~N}$ when placed in this field. What is the magnitude of the electric field? 
$1.5 \times 10^3 \mathrm{~N} / \mathrm{C}$