A particle with charge $-9C$ is located on the $x-$axis at the point $-6cm,$ and a second particle with charge $-4C$ is placed on the $x-$axis at $10cm.$

What is the magnitude of the total electrostatic force on a third particle with charge $7C$ placed on the $x-$axis at $2cm?$ The Coulomb constant is $8\mathrm{.}9875{10}^{9}N*\frac{m^2}{C^2}.$ Answer in units of $N.$