An unknown positive point charge is placed at x = -0.26 m, y = 0 m, a charge of -3.4 micro-coulombs is placed at x = 0 m, y = -0.5 m, a charge of +3.4 micro-coulombs is placed at x = +0.22 m, y = -0.44 m, and charge of +3.4 micro-coulombs is placed at x = 0 m, y = +0.5 m. If the total electric field due to all four charges at the origin is 3.7 x 106 N/C (the x component of the total electric field is positive), what is value of the magnitude of the unknown charge in micro-coulombs? If negative, include a negative sign.