Question

which angle is vertical to ∠5? ∠9, ∠10, ∠7, ∠3 (with a diagram of intersecting lines and numbered angles)

Explanation:

Vertical angles are pairs of opposite, non-adjacent angles formed by intersecting straight lines. For $\angle 5$, it is formed by two intersecting lines, and its opposite non-adjacent angle is $\angle 7$.

Answer:

$\angle 7$