（1）2.6+3.4x=23

               3.4x=23-2.6

                   x=6（2）12.3÷x=8.2

                  x=12.3÷8.2

                  x=1.5

（3）2x-12+3=26

                  2x=35

                   x=17.5（4）21.3x-18.8x=1

                     2.5x=1

                         x=0.4