The missing justification is for the statement that three angles add to a particular angle. The appropriate choice is ...
... c. Angle Addition Postulate
-4b-8 + -1b^2 +2b^3
-4(-2)-8+-1(-2)^2+2(-2)^3
8-8+2^2-4^3
4-64
60
F and E are congruent with the figure above
17x= 13 and 8 are both y's so you combine them by subtracting 13 from both sides and then you have 17x=-5y
