Problem 407. Circle, Angle, Tangent, Perpendicular, Secant, Radius, Center. Level: High School, College, SAT Prep.

Lines ABC and AD are tangent to circle O (B, D tangency points). Line CEFG is perpendicular to AD and H is the intersection of AF and circle O. If the measure of angle OEC is equal to 140 degrees, find the measure of angle AHD.