Question

which angle is vertical to ∠efa?

Explanation:

Step1: Recall vertical - angle definition

Vertical angles are formed when two lines intersect. They are opposite each other and have equal measures.

Step2: Identify intersecting lines

Lines $AE$ and $BC$ intersect at point $F$.

Step3: Determine vertical angle to $\angle EFA$

The angle vertical to $\angle EFA$ is $\angle BFC$ since they are opposite each other at the intersection of the two lines.

Answer:

$\angle BFC$