In a cement manufacturing unit, 36 tonne/h of calcite of 5-cm size is fed to a gyratory crusher. Screen analysis from the crusher shows a surface area of product of 61.7 2/. The crushed material is then subjected to fine reduction in a hammer mill. Mill product analysis indicates a surface area of 740 2/. Rittingers number for calcite is 75.9 2 /kJ. Efficiency of the grinder is 30%. The crusher and grinder are driven on the same shaft (by an electric motor) whose transmission efficiency is 90%. If 480 hp is fed at the other end of the shaft, compute the efficiency of the crusher.