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 d? (2x + 16) + (6x − 4) = 90 (x + 16) − (x) = 90 (x + 16) + (2x + 16) = 180 (2x + 16) + (x) = 180