An electric utility owns and operates four coal-fired power plants. These power plants have the following SO2 emission factors and fuel heat input: Plant 1: 5931 tons/year, 10.56x1012 BTU/year heat input Plant 2: 5523 tons/year, 19.62x1012 BTU/year heat input Plant 3: 5611 tons/year, 40.17x1012 BTU/year heat input Plant 4: 4006 tons/year, 91.75x1012 BTU/year heat input What is the average emission factor for this electric utility, in lb SO2/106 BTU? Report 3 significant figures and report unit as lb SO2/10^6 BTU