$${ L }^{ 2 } -9L=-3x+5$$
$x=-\frac{L^{2}}{3}+3L+\frac{5}{3}$
$L=\frac{\sqrt{101-12x}+9}{2}$
$L=\frac{-\sqrt{101-12x}+9}{2}$
$L=\frac{\sqrt{101-12x}+9}{2}$
$L=\frac{-\sqrt{101-12x}+9}{2}\text{, }x\leq \frac{101}{12}$