3x - 6 = 9

移项：3x = 9 + 6

除以3：x = （9 + 6） / 3

解得：x = 5

20 + 5x = 95

移项：5x = 95 - 20

除以5：x = （95 - 20） / 5

解得：x = 15

1.2x = 6

除以1.2：x = 6 / 1.2

解得：x = 5

45 ÷ 2x = 5

移项：45 = 5 * 2x

除以10：x = 45 / 10

解得：x = 4.5

7 + x = 7

移项：x = 7 - 7

解得：x = 0

100 - x = 90

移项：x = 100 - 90

解得：x = 10

x ÷ 45 = 4.5

乘以45：x = 4.5 * 45

解得：x = 202.5

x + 3.5 = 10

移项：x = 10 - 3.5

解得：x = 6.5

6.8 ÷ x = 1.7

乘以x：6.8 = 1.7 * x

除以1.7：x = 6.8 / 1.7

解得：x = 4

1 - x = 0.31

移项：x = 1 - 0.31

解得：x = 0.69

这些方程的解答过程展示了基本的代数操作，包括移项、合并同类项、除法和乘法。希望这些解答对你有所帮助。