（1）3x-60=31.8

              3x=91.8

                x=30.6

                 5x=9

                   x=1.8（3）（x+3）÷2=6

                      x+3=12

                          x=9

（4）x÷2 +1.8=3.9   

                 x÷2=2.1

                       x=4.2（5）1.7x +9×3=30.4

                    1.7x=3.4

                         x=2（6）8x-3x=46. 5

              5x=46.5

                x=9.3