The answer is : B
-Hope this helps, even though you asked for no explanation.
Answer:

Step-by-step explanation:
We know that in a sequence of ten terms, each term (starting with the third term) is equal to the sum of the two previous terms. The seventh term is equal to 6. Therefore, we have

We know that:

We get:

Therefore, we calculate

12.9 = x + 7.1
subtract 7.1 from both sides to isolate the variable, x.
5.8 = x
5.8 is your answer.
To solve your question, you add all of the measurements together, set them equal to 180, solve for x, and plug x back in for whichever angle they are asking for; in this case, they want angle R
7x + 12x + 20 + 20x - 35 = 180
39x - 15 = 180
39x = 180 + 15
39x = 195
x = 5
Angle R = 12x + 20
12(5) + 20
60 + 20
80
Option C is your answer.