人教版五年级上册数学同步的40和41面的解下面方程不知道做?

（X-12）÷4=4.5 4.5X+X=23.1 12X+24X-15X=147
X-12=18 5.5x =23.1 21x =147
x =30 x=4.2 x =7
希望采纳意见

（X-12）÷4=4.5
(X-12) ÷4*4=4.5*4
X-12+12=18+12
X=30
4.5X+X=23.1
5.5X÷5.5=23.1÷5.5
x=4.2
12X+24X-15X=147
(12+24-15)X=147
21X÷21=147÷21
x=7

（X-12）÷4=4.5 4.5X+X=23.1 12X+24X-15X=147
X-12=18 5.5x =23.1 21x =147
x =30 x=4.2 x =7