a) $4x - 10 = 0$
⇔ $2( 2x - 5 ) = 0$
⇔ $2x - 5 = 0$
⇔ $x = \dfrac{5}{2}$
$S =$ { $\dfrac{5}{2}$ }
b) $2x + x + 12 = 0$
⇔ $3x = -12$
⇔ $x = -4$
$S =$ { $-4$ }
c) $x - 5 = 3 - x$
⇔ $x + x = 3 + 5$
⇔ $2x = 8$
⇔ $x = 4$
$S =$ { $4$ }
d) $2x - ( 3 - 5x ) = 4( x +3)$
⇔ $2x - 3 + 5x = 4x + 12$
⇔ $7x - 4x = 12 + 3$
⇔ $3x = 15$
⇔ $x = 5$
$S =$ { $5$ }
e)$ 2t - 3 + 5t = 4t + 12$
⇔ $7t -4t = 12 + 3$
⇔ $3t = 15$
⇔ $t = 5$
$S =$ { $5$ }
f) $3 - 4x + 24 + 6x = x + 27 + 3x$
⇔ $-4x + 6x - 3x - x = 27 -3-24$
⇔ $-x = 0$
⇔ $x= 0$
$S =$ { $0$ }