A centrifugal clutch, transmitting 20 kW at 750 rpm consists of four shoes. The clutch is to be engaged at 75% of the running speed. The inner radius of the drum is 165 mm, while the radius to the center of gravity of the shoe, when the clutch is engaged, is 140 mm. The coefficient of friction is 0.25. The mass of each shoe is (a) 6 kg (c) 2 kg (b) 8 kg (d) 4 kg