ABCD is a quadrilateral inscribed in a circle, as shown below: Circle O is shown with a quadrilateral ABCD inscribed inside it. Angle A is labeled x plus 16. Angle B is labeled x degrees. Angle C is labeled 6x minus 4. Angle D is labeled 2x plus 16. What equation can be used to solve for angle C? (x + 16) + (x) = 180 (x + 16) + (6x − 4) = 180 (x + 16) − (2x + 16) = 180 (x + 16) + (x) = 90