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12 + 3 x = 7 x + 10

3 x - 7 x = 10 - 12

- 4 x = - 2

x = 2

- 3 x - 4 = 5 + x

- 3 x - x = 5 + 4

- 4 x = 9

x = - 9/4

4 x - 9 = - 6 + 12 x

4 x - 12 x = - 6 + 9

- 8 x = 3

x = - 3/8

2 + 5 x = - 2 x - 3

5 x + 2 x = - 3 - 2

7 x = - 5

x = - 5/7

4 x - 1 = 14 + x

4 x - x = 14 + 1

3 x = 15

x = 15/3 = 5

continue