A test charge of -5.0 X 10-7 C is placed between two other charges so that it is 50 mm from a charge of -3.0 X 10-7 C and 10 cm from a charge of -6.0 X 10-7 C. The three charges lie along a straight line. What is the magnitude and direction of the force on the test charge?
magnitude: a) 0.27 N b) 1.63 N c) 5.91 N d) 10.8 N