（1）9x-1.8=5.4
     9x-1.8+1.8=5.4+1.8
             9x=7.2
          9x÷9=7.2÷9
              x=0.8
（2）x-0.5x=0.5
       0.5x=0.5
  0.5x÷0.5=0.5÷0.5
          x=1．