1) $x + 12 = -5 - x$
$\Leftrightarrow x + x = -5 - 12$
$\Leftrightarrow 2x = -17$
$\Leftrightarrow x = -\dfrac{17}{2}$
2) $x + 5 = 10 - x$
$\Leftrightarrow x + x = 10 - 5$
$\Leftrightarrow 2x = 5$
$\Leftrightarrow x = \dfrac{5}{2}$
3) $2(x - 1) + 3(x - 2) = x - 4$
$\Leftrightarrow 2x - 2 + 3x - 6 = x - 4$
$\Leftrightarrow 5x - 8 = x - 4$
$\Leftrightarrow 5x - x = -4 + 8$
$\Leftrightarrow 4x = 4$
$\Leftrightarrow x = 1$
