Two point charges are placed on the $x$ -axis as follows: Charge $q_{1}=+4.00 \mathrm{nC}$ is located at $x=0.200 \mathrm{~m},$ and charge $q_{2}=+5.00 \mathrm{nC}$ is at $x=-0.300 \mathrm{~m} .$ What are the magnitude and direction of the total force exerted by these two charges on a negative point charge $q_{3}=-6.00 \mathrm{nC}$ that is placed at the origin?