In a certain region, the earth's magnetic field has a magnitude of 4.7e-5T and is directed north at an angle of 61* below the horizontal. An electrically charged bullet is fired North and 15* above the horizontal, with a speed of 640m/s. The magnetic force on the bullet is 3.6e-10N, directed due east. Determine the bullet's electric charge(q), including its algebraic sign(+/-).