（1）x-80%x=40

           20％x=40

                 x=200（2）24%x+7=7.24

            24％x=0.24

                   x=1（3）（1-75%）x=5

                  25％x=5

                         x=20（4）x+5%x=8.4

         105％x=8.4

                   x=8

（5）18-150%x=7.5

             150％x=10.5

                     x=7（6）x+60%x=14.4

          160％x=14.4

                   x=9（7）55％x-20%x=280

                  35％x=280

                         x=800（8）1.2x+30%x=45

                   1.5x=45

                       x=30