ANSWER
A) 70º
EXPLANATION
In quadrilaterals inscribed in a circle, opposite angles are supplementary - their measures add up 180º. Therefore:
[tex]\begin{gathered} m\angle DAB+m\angle DCB=180º \\ 110º+m\angle DCB=180º \\ m\angle DCB=180º-110º \\ m\angle DCB=70º \end{gathered}[/tex]
