Answer
reference angle = $60^o$
Refer to the image below for the drawing.
Work Step by Step
The angle is negative so from the positive x-axis, move $300$ degrees clockwise.
(refer to the attached image in the answer part above)
The terminal side of the angle is in Quadrant I.
The reference angle of an angle is the smallest acute angle that the terminal side makes with the x-axis.
Thus, the reference angle of the given angle is:
$=360^o -300^o
\\=60^o$