In a certain region, the earth's magnetic field has a magnitude of 4.7 x 10-5 T and is directed north at an angle of 42° below the horizontal. An electrically charged bullet is fired north and 14° above the horizontal, with a speed of 560 m/s. The magnetic force on the bullet is 2.6 x 10-10 N, directed due east. Determine the bullet's electric charge, including its algebraic sign (+ or -).