Answer
1. given
2. Corresponding $\angle$s are $\cong$
3. Vertical $\angle$s are $\cong$
4. $\angle$ 3 $\cong$ $\angle$4
5.$\angle$ 1 $\cong$ $\angle$4
Work Step by Step
1. Given
2. If two parallel line l and m cut by transversal t, then corresponding angles of 1 and 2 are congruent
3. By theorem all vertical angles are congruent
5. By theorem of transitive, if $\angle$1 $\cong$ $\angle$ 2, then $\angle$2 $\cong$ $\angle$ 3 therefore $\angle$1 $\cong$ $\angle$ 3
