Let's imagine a point E in the line DA and at the left of point A.
From the formula to find the angle between a tangent and a chord:
[tex]m\angle CAE=\frac{1}{2}m\angle CBA[/tex]
The measure of angle ABC is given: 220°. Then:
[tex]\begin{gathered} m\angle CAE=\frac{1}{2}\cdot220^o \\ m\angle CAE=110^o \end{gathered}[/tex]
Now, from the figure, we can see that angles CAE and CAD form an angle of 180°. Then:
[tex]m\angle CAD+m\angle CAE=180^o[/tex]
Replacing values and solving:
[tex]\begin{gathered} m\angle CAD+110^o=180^o \\ m\angle CAD=180^o-110^o \\ m\angle CAD=70^o \end{gathered}[/tex]
Then, finally, the measure of angle CAD is 70°.
