## Elementary Geometry for College Students (5th Edition)

$\angle$3=87$^{\circ}$
If two parallel lines are cut by a traversal, then the pairs of opposite angles are congruent. Since we are given that lines r and s are parallel, and $\angle$2 and $\angle$3 are opposite angles, we know that $\angle$2 and $\angle$3 are congruent. Since $\angle$2=87$^{\circ}$, $\angle$3 must also be 87$^{\circ}$.