Problem 10-38 Addition of Electric fields - A

Two negative charges have locations as shown in the Figure. Charge $q_1$ is  $-3.6\times 10^{-8} C;$ charge $q_2$ is  $-5.2 \times10^{-8} C.$ What is the electric field (magnitude and direction) at (a) $\text{point A}$? (b) $\text{point B}$?

No. To determine the direction of the field at $A$ due to $q_1$ we imagine placing a small test charge at $A$ and observing the direction of the force on it. The charge should be Positive or Negative choose one.