注以下东东都是我自己算的你自己最好先算算 7χ－2×9＝806x－4x＝20.2 （χ+12）÷4＝4.5解:7x-18=80解:2x=20.2解:(x+12)/4*4=4.5*47x-18+18=80-+18 2x/2=20....