Answer
$US = \frac{\sqrt{3}}{3}$
Work Step by Step
$\frac{US}{OS} = tan ~30^{\circ}$
$\frac{US}{OS} = \frac{1}{\sqrt{3}}$
$US = \frac{OS}{\sqrt{3}}$
$US = \frac{1}{\sqrt{3}}$
$US = \frac{\sqrt{3}}{3}$
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