13.2x+9x=33.3
(13.2+9)x=33.3
22.2x=33.3
x=33.3/22.2=1.5

8x-3x=105
(8-3)x=105
5x=105
x=105/5
x=21.
5.4x+x=12.8（也是这样算）5.4x+x=12.8(5.4+1)x=12.86.4x=12.8x=12.8/6.4x=2