先去括号得60X=1680-80X,移项得140X=1680,X=12
60x=1680-80x60x+80x=1680140x=1680x=12
60x=80(21-x)60x=1680-80x140x=1680x=12
解 60=1680-80x 60x+80x=1680 140x=1680 x=12
