原式=[0.75×42.7-57.3×0.25+57.3×1]÷3×7972 =[0.75×42.7-（1-0.25）×57.3]÷3×7972 =[0.75×（42.7+57.3）]÷3×7972 =0.75×100÷3×7972 =75÷3×7972 =25×7972 =19...