To determine the marked letters of an angle:
Intersecting lines are straight lines that meet or crosses each other at a certain point.
Vertical angles are pair angles formed when two lines intersect. Vertical angles are sometimes referred to as vertically opposite angles because the angles are opposite to each other.
[tex]\begin{gathered} C=\text{ 110 (vertical opposite angle)} \\ C=D \\ \text{Hence C=D=110}^0 \end{gathered}[/tex]
Since the lines are parallel the marked angles C = D = 110
