Answer:
a
Step-by-step explanation:
r and t are same- side exterior angles and sum to 180 , so
t + r = 180 , that is
t + 91 = 180 ( subtract 91 from both sides )
t = 89
t and u are vertically opposite angles and are congruent , so
u = t = 91
Then
t + u = 89 + 89 = 178 → a
