Answer
$x = 6$ units.
Work Step by Step
1. Use the area formula
$A = \frac{1}{2}absin(C)$
$18\sqrt {3} = (\frac{1}{2})(x)(2x)sin(60)$
$18\sqrt {3} = (\frac{1}{2})(2x^{2})sin(60)$
$18\sqrt {3} = (\frac{2x^{2}sin(60)}{2})$
$18\sqrt {3} = x^{2}sin(60)$
$x^{2} = \frac{18\sqrt {3}}{sin(60)}$
by GDC / calculator
$x^{2} = 36$
$x = ±\sqrt {36}$
$x = ±6$ units
Since $x \ne -6$ units, then the only answer is $x = 6$ units.
