In a Hall-effect experiment, a current of 3.5 A is sent lengthwise through a conductor 0.84 cm wide, 3.8 cm long, and 8.1 μm thick, producing a transverse (across the width) Hall potential difference of 9.9 μV when a magnetic field of 2.0 T is passed perpendicularly through the thickness of the conductor. From these data, find (a) the drift speed of the charge carriers and (b) the number density of charge carriers.