Calculate the value of x

Angle AOB = 2x + 28. An angle at the circumference is half that at the centre, so angle ACB = x + 14. Opposite angles of a cyclic quadrilateral sum 180° , so ACB + ADB = 180. ADB is given as 3x - 70. This combines to x + 14 + 3x - 70 = 180, which simplifies to 4x = 236, so x = 59°. To check this is of a reasonable size this can be substituted into the formulas for AOB and ADB to give an obtuse angle, as expected.