Answer
$x\approx 5.94$
Work Step by Step
First lets find $\angle B $
$\angle A+\angle B+\angle C=180^0\Rightarrow 30^0+80^0+\angle B\Rightarrow \angle B=180^0-\left( 80^0+30^0\right) =70^0$
From the law of sines
$\dfrac {x}{\sin 30}=\dfrac {10}{\sin \angle B}\Rightarrow \dfrac {x}{\dfrac {1}{2}}=\dfrac {10}{\sin 70}\Rightarrow x=\dfrac {5}{\sin 70}\approx 5.94$
