28.5 . A -4.80 uC charge is moving at a constant speed of 6.80 X 10' m/s in the +x-direction relative to a reference frame. At the instant when the point charge is at the origin, what is the magnetic- field vector it produces at the following points: (a) x = 0.500 m, y = 0, z = 0; (b) x = 0, y = 0.500 m, z = 0; (c) x = 0.500 m, y = 0.500 m, z = 0; (d) x = 0, y = 0, z = 0.500 m