First of all, angle 4 is not congruent to angle 7 because of same side interior angles. They are congruent because they are corresponding angles. Next, where it says supplementary angles theorem, that is incorrect because the answer is supposed to be angle addition postulate. Lastly, it isnt the transitive propety but it is actually the substitution propert of equality because you substitute angle 7 with angle 4. Hope this helps...
