Elementary Geometry for College Students (6th Edition)

m$\angle$3=68.3$^{\circ}$
If two parallel lines are cut by a transversal, then the pairs of opposite angles are congruent. Since we are given that lines l and m are parallel, and $\angle$2 and $\angle$3 are opposite angles, we know that $\angle$2 and $\angle$3 are congruent. Since $\angle$2=68.3$^{\circ}$, $\angle$3 must also be 68.3$^{\circ}$.