A = 121, Vertical Angles Theorem
B = 59, Supplementary Angles Theorem
C = 59, Vertical Angles Theorem
D = 55, Alternate Interior Angles Theorem
E = 4, sum of all angles in a triangle is 180
F = 73, sum of all angles in a triangle is 180
G = 73, Alternate Interior Angles Theorem
H = 48, Alternate Interior Angles Theorem
I = 4, Alternate Interior Angles Theorem