Answer
reference angle = $30^o$
Refer to the image below for the drawing.
Work Step by Step
The angle is positive so from the positive x-axis, move 210 degrees counterclockwise.
(refer to the attached image in the answer part above)
The terminal side of the angle is in Quadrant III.
The reference angle of an angle $\theta$ in Quadrant III can be found using the formula $\theta - 180^o$
Thus, the reference angle of the given angle is:
$=210^o - 180^o
\\=30^o$
