Label the radii as OA and OB (OAB = 60) respectively, intersection between OB and tangent is D.
Because they are radii, OA = OB, and since OAB = 60 <=> OAB is an equilateral triangle <=> AOB = 60
OA is perpendicular to the tangent <=> OAD is a right triangle.
<=> x = 90 - AOB = 90 - 60 = 30
