2. A cross belt arrangement has centre distance between pulleys as 1.5 m. The diameter of bigger and smaller pulleys are 'D' and 'd' respectively. The smaller pulley rotates at 1000 rpm, and the bigger pulley at 500 rpm. The flat belt is 6 mm thick and transmits 7.5 kW power at belt speed of 13 m/s approximately. The coefficient of belt friction is 0.3 and the density of belt material is 950 kg/ml. If the permissible tensile stress for the belt material is 1.75 MPa, calculate: 

a. Diameters of pulleys. 

b. Length and width of belt.