this is an ange formed by two intersecting chords
then the missing angle is given by
[tex]\theta=\frac{1}{2}(arcCB+arcSD)[/tex][tex]\theta=\frac{1}{2}(191+55)[/tex][tex]\theta=\frac{1}{2}(246)[/tex][tex]\theta=123\degree[/tex]
the missing angle is 123°
