a whale swims due east for a distance of 6.9 km turns around and goes due west for 1.8 km and finally turns around again and heads 3.7 km due east

Two point charges lie on the x axis. a charge of + 2.30 pc is at the origin, and a charge of − 4.50 pc is at x=−11.0cm. what third charge should be placed at x=+26cm so that the total electric field at x=+13.0cm is zero? express your answer to three significant figures and include appropriate units.