a)
[tex]2(x + 3) = 12 + x \\ 2x + 6 = 12 + x \\ x = 6[/tex]
b)
[tex]3(2 - x) + 2 = 3 - \frac{1}{2} (x + 1) \\ 6 - 3x + 2 = 3 - \frac{1}{2} (x + 1) \\ 8 - 3x = 3 - \frac{1}{2} x - \frac{1}{2} | \times 2 \\ 16 - 6x = 6 - x - 1 \\ - 5x = 5 - 16 \\ - 5x = - 11 | \div ( - 5) \\ x = \frac{11}{5} \\ x = \frac{22}{10} \\ x = 2.2[/tex]