Answer:
![(3x+14)+(8x-21)=180°](https://img.qammunity.org/2020/formulas/mathematics/high-school/4gad9ektm7g8z3rg9e6e6i60ep7n9q79d7.png)
Explanation:
Angles with measures
and
(or pmore precisely, vertical angle to angle 8x-21) are supplementary (add up to 180°).
Converse to same-side interior angles theorem states that If two same-side interior angles are supplementary, then l║p.
So, to prove that lines l and p are parallel, you have to show that angles
and
are supplementary.
Thus,
![(3x+14)+(8x-21)=180°](https://img.qammunity.org/2020/formulas/mathematics/high-school/4gad9ektm7g8z3rg9e6e6i60ep7n9q79d7.png)