## Elementary Geometry for College Students (6th Edition)

m$\angle$6 = 71$^{\circ}$
Postulate says that if two parallel lines are cut by a transversal, then the pairs of alternate angles are congruent. Since we are given that lines l and m are parallel, and $\angle$3 and $\angle$6 are alternate angles, we know that $\angle$3 and $\angle$6 are congruent. Since $\angle$3=71$^{\circ}$, $\angle$6 must also be 71$^{\circ}$.