（1）8+4x=10

8+4x-8=10-8

4x=2

4x÷4=2÷4

x=0.5

（2）5x-1.6×0.5=30.8

5x-0.8=30.8

5x-0.8+0.8=30.8+0.8

5x=31.6

5x÷5=31.6÷5

x=6.32

（3）1.4x+2.1x=70

3.5x=70

3.5x÷3.5=70÷3.5

x=20

（4）（x-13.8）÷6=9.2

（x-13.8）÷6×6=9.2×6

x-13.8=55.2

x-13.8+13.8=55.2+13.8

x=69