7x-x+2*3=29.4
7x-x=29.4-2*3
6x=23.4
x=23.4÷6
x=1.9
（28.8+5.5x+3.2）/2＝71
28.8+3.2+5.5x=71×2
32+5.5x=142
5.5x=142-32
5.5x=110
x=110÷5.5
x=20