Question

which angle number represents an angle vertical to ∠cgb?

Explanation:

Step1: Recall vertical - angle definition

Vertical angles are formed when two lines intersect. They are opposite each other.

Step2: Identify intersecting lines

Lines $AB$ and $CD$ intersect at point $G$.

Step3: Find vertical angle to $\angle CGB$

The angle vertical to $\angle CGB$ is $\angle AGD$. In terms of the numbered angles, $\angle CGB$ and $\angle AGD$ are vertical angles, and $\angle AGD$ is angle number $3$.

Answer:

$3$