A "Hall bar" specimen is 250 mm long, 12 mm wide, and 1.5 mm thick. Along the 250 mm direction (+x), +5 V drives a current of +1.75 mA. Along the 1.5 mm direction (+z) a magnetic field of 1 Tesla is applied. This causes a voltage across the 12 mm direction (+y) of -7.5mV.
Find the a) carrier mobility, b) carrier density, and c) carrier charge sign.