In Hall Effect measurements a plate of width h = 10 mm and length l = 50 mm made of p-type semiconductor was placed in a magnetic field with induction B = 5.0kG. A potential difference V =10V was applied across the edges of the plate. In this case the Hall field is VH = 50 mV and resistivity p = 2.5Ω.cm. Find the concentration of holes and hole mobility.