A particle is shot at a velocity of \(3 \times 10^{4} \mathrm{~m} / \mathrm{s}\) to the right and enters the magnetic field generated by a large, flat current-carrying sheet. The current in the sheet is parallel to the particle's initial line of motion. The particle exits the magnetic field \(6.8 \mathrm{~cm}\) directly above the location where it enters.

(a) Is the particle's charge positive or negative?

(b) If the sheet carries a current of \(4 \mathrm{~A}\) per unit width, what is the ratio of the charge on the particle to its mass?