(4.5-x)*7=17.5
4.5*7-7x=17.5
4.5*7-17.5=7x
7x=14
x=2
(5.5-1.3)x=12.6
4.2x=12.6
x=3
0.8x=10.5-0.5*13
0.8x=4
x=5
4*5(x-0.3)=3*8
20x=3*8+20*0.3
20x=30
x=1.5
等号要对齐