posted by BM .
Two charges are placed on the x axis. One of the charges (q1 = +6.14C) is at x1 = +3.00 cm and the other (q2 = -28.6C) is at x2 = +9.00 cm. Find the net electric field (magnitude and direction given as a plus or minus sign) at (a) x = 0 cm and (b) x = +6.00 cm.
At x = 0, charge q1 creates an electric field in the -x direction and charge q2 creates an electric field in the +x direction. Use the Coulomb equation
E = kq/r^2
for the E fields and add them, taking the sign into account.
At x = 6.00 cm, you are between q1 and q2, and the E fields due to the two charges are in the same direction (+x).