1. The problem asks to identify which pair of angles are alternate interior angles when two parallel lines are cut by a transversal. 2. **Definition:** Alternate interior angles are pairs of angles that lie between the two parallel lines but on opposite sides of the transversal. 3. Given the lines $n$ and $m$ are parallel and cut by a transversal, the alternate interior angles are the pairs that are inside the parallel lines and on opposite sides of the transversal. 4. From the diagram, angles 3 and 6 are on opposite sides of the transversal and between lines $n$ and $m$. 5. Therefore, the pair of alternate interior angles is **angle 3 and angle 6**. **Final answer:** Angle 3 and angle 6 are alternate interior angles.