The answer to the first part is D
Answer:
Given : s||t
Exterior sides in opposite rays : ∠5 and ∠7 are supplementary
Definition of supplementary angles : m∠5 + m∠7 = 180°
If lines are ||, corresponding angles are equal : m∠1 = m∠5
Substitution : m∠1 + m∠7 = 180°
Answer: 19.5 is the answer
Step-by-step explanation: 39 divided by 2 is 19.5
Answer:

Step-by-step explanation:
Recall that
. Using this, we can simplify and combine the two terms:
. Therefore, the terms may be combined.