（1）2.6+3.4x=23

                3.4x=20.4

                    x=6（2）6.3x-x=15.9

            5.3x=15.9

                 x=3（3）4（x-2.05）=7.8

                 x-2.05=1.95

                        x= 4

（4）4.98-2.3x=1.3

                2.3x=3.68

                     x=1.6

 （5）17.6x-4×0.6=6.4

              17.6x-2.4=6.4

                    17.6x=8.8

                           x=0.5（6）15.3x-12.8x=10

                    2.5x=10

                        x= 4