解方程(5 + x)/40 = x/30
问题描述：
解方程(5 + x)/40 = x/30
答
(5+x)*30=40x
150+30x=40x
10x=150
x=15
答
(5 + x)/40 = x/30
1/8=x/30-x/40
1/8=x/120
x=120/8
x=15
答
(5 + x)/40 = x/30 两边乘120
3（5+x）=4x
15+3x=4x
4x-3x=15
x=15