x+120=5x 急,

x+120=5x 急,
x+120=5x 急,

x+120=5x 急,
120=5x-x
120=4x
x=30

x+120=5x
x-5x=-120
-4x=-120
x=-120/-4=30

这个很简单啊。
x+120=5x
120=5x-x
120=4x
可易解得 x=30

x+120=5x
x-5x=-120
-4x=-120
x=30

x=120/(5-1)
x=30

x+120=5x
5x-x=120
4x=120
x=120除以4
x=30

x+120=5x
移项得：4x=120
两边各除以4得：x=30