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.