If all cars in the usa ran with petrol blended with 20% bioethanol produced by enzymatic hydrolysis of cellulosic feedstock, what would be the annual reduction in co2 production in tonnes? take usa annual petrol consumption to be 5*10^11 litres, density of petrol to be 0.73kg/litre, density of ethanol to be 0.79kg/litre heat combustion of ethanol and petrol to be 29.5MJ/kg, 43.5MJ/kg respectively.