Answer
$$ x=20 ^{\circ} , \ 40^{\circ},\ 140^{\circ},\ 160^{\circ},\ 260^{\circ},\ 280^{\circ} $$
Work Step by Step
Given $$ \sin 3x= \frac{\sqrt{3} }{2}$$
From the figure, we find the intersection points between $y= \sin 3x$ and $ y=\frac{\sqrt{3} }{2}$; we get
$$ x=20 ^{\circ} , \ 40^{\circ},\ 140^{\circ},\ 160^{\circ},\ 260^{\circ},\ 280^{\circ} $$
