$\frac{3x -7}{4x +2} = \frac{3x -14}{4x -13}$ $(ĐKXĐ:$ $x \neq \frac{1}{2}; x \neq \frac{13}{4})$
$⇔ (3x -7).(4x -13) = (3x -14).(4x +2)$
$⇔ 12x² -67x +91 = 12x² -50x -28$
$⇔ 12x² -12x² -67x +50x = -28 -91$
$⇔ -17x = -119$
$⇔ x = 7$ $(T/m$ $đkxđ)$
$Vậy$ $S =$ {$7$}