\[\begin{aligned} &6x = 4x - 9& \\ \iff &6x - 4x = -9& \\ \iff &2x = -9& \\ \iff &x = -\dfrac 9 2&. \end{aligned}\] Donc $S = \left\{-\dfrac 9 2\right\}$.

\[\begin{aligned} &6-8x = 16x& \\ \iff &-8x - 16x = -6& \\ \iff &-24x = -6& \\ \iff &x = \dfrac{-6}{-24}& \\ \iff &x = \dfrac 1 4.& \end{aligned}\] Donc $S = \left\{\dfrac 1 4\right\}$.

\[\begin{aligned} &3x - 2 = 11& \\ \iff &3x = 11 + 2& \\ \iff &3x = 13& \\ \iff &x = \dfrac{13} 3.& \end{aligned}\] Donc $S = \left\{\dfrac{13} 3\right\}$.

\[\begin{aligned} &5-7x= -11& \\ \iff &-7x = -11 - 5& \\ \iff &-7x = -16& \\ \iff &x = \dfrac{-16}{-7}& \\ \iff &x = \dfrac{16}7.& \end{aligned}\] Donc $S = \left\{\dfrac{16}{7}\right\}$.

\[\begin{aligned} &4x - 7 = 3x + 8& \\ \iff &4x - 3x = 8 + 7& \\ \iff &x = 15.& \end{aligned}\] Donc $S = \big\{15\big\}$.

\[\begin{aligned} &9x + 5 = 4 - 3x& \\ \iff &9x + 3x = 4 - 5& \\ \iff &12x = -1& \\ \iff &x = -\dfrac 1 {12}.& \end{aligned}\] Donc $S=\left\{-\dfrac 1 {12}\right\}$.

\[\begin{aligned} &7 - 8x = 11x - 5& \\ \iff &-8x - 11x = -5 - 7& \\ \iff &-19x = -12& \\ \iff &x = \dfrac{-12}{-19}& \\ \iff &x = \dfrac{12}{19}.& \end{aligned}\] Donc $S = \left\{\dfrac{12}{19}\right\}$.

\[\begin{aligned} &-2x+5 = -8x + 10& \\ \iff &-2x + 8x = 10 - 5& \\ \iff &6x = 5& \\ \iff &x = \dfrac 5 6.& \end{aligned}\] Donc $S = \left\{\dfrac 5 6\right\}$.