The missing reason to complete Hector's proof is
<span>Corresponding Parts of Congruent Triangles Are Congruent
It's been established in the previous statement that triangle LNO and triangle PNM are congruent by the AAS Postulate.
The proof
</span>Corresponding Parts of Congruent Triangles Are Congruent
is comprehensive.
The slope of the line is delta y / delta x, so the answer is: -1/3.
Plot these points
vertex: (-4,-7)
x intercepts: (-5.5,0), (-2.5, 0)
and those two other points
the graph should look something like this: