Ikeep getting it wrong and i can't move on to the next part! you need to look at both pictures to answer this.

Explanation:

3. ∠2 and ∠3 are a linear pair → definition of a linear pair

4. ∠3 and ∠4 are a linear pair → definition of a linear pair

5. m∠2 +m∠3 = 180° → definition of a linear pair (or angle addition postulate)

6. m∠3 +m∠4 = 180° → definition of a linear pair (or angle addition postulate)

7. m∠2 +m∠3 = m∠3 +m∠4 → substitution property

8. m∠2 = m∠4 → subtraction property

9. ∠2 ≅ ∠4 → definition of congruent angles

A pair of angles is a "linear pair" if they are adjacent and supplementary. ∠2 and ∠3 are adjacent and the non-common legs form a straight line. It isn't clear what your definition of linear pair is and what you need to do to claim that the angles sum to 180°. Above, we have assumed a definition of "linear pair" that includes the facts that → they sum to 180°; → non-adjacent sides form a straight line.