The mass required for metallurgical test work on a copper ore is estimated to be 130.6 kg. If at a confidence level of 0.2 Cu at 2 standard deviation, the copper assay is 9% and the liberation size for the copper mineral (chalcocite) is 106 m. What was the lower size if the top size was 2.8cm. (Assume the densities of chalcocite and the gangue as 5.6 g/cm3 and 2.5 g/cm3).