3(5x+20)=45x
===> 5x+20=45x÷3
===> 5x+20=15x
===> 15x-5x=20
===> 10x=20
===> x=2这道会做吗
90-7x=23x-30
还要验算哦90-7x=23x-30
===> 90+30=23x+7x
===> 120=30x
===> x=4
代入得到：左边=90-7×4=62；右边=23×4-30=62
左边=右边
所以，x=4是原方程的解