Answer
$x$ = -$\frac{2}{3}s$ + $\frac{4}{3}t$
Work Step by Step
3$x_{1}$ + 2$x_{2}$ - 4$x_{3}$ = 0
3$x_{1}$ = -2$x_{2}$ + 4$x_{3}$
$x_1$ = -$\frac{2}{3}x_{2}$ + $\frac{4}{3}x_3$
Now add parameters for $x_1$, $x_2$, and $x_3$.
So, $x_1$ = $x$ ; $x_2$ = $s$ ; $x_3$ = $t$
$x$ = -$\frac{2}{3}s$ + $\frac{4}{3}t$