1.6x+4(20-x)=104
6x+80-4x=104
2x=24
x=12
2.24-2(x-2)=70-6x
24-2x+4=70-6x
6x-2x=70-24-4
4x=42
x=10.5
3.12+2（5x-7）=70-8x
12+10x-14=70-8x
10x+8x=70-12+14
18x=72
x=4