Answer: 35 (choice C)
=============================================
Step-by-step explanation:
For any triangle, the three interior angles always add to 180.
D+E+F = 180
(7b+1) + (2b+1) + (b+8) = 180
(7b+2b+b) + (1+1+8) = 180
10b+10 = 180
10b = 180-10
10b = 170
b = 170/10
b = 17
Use this value of b to find the three angle measures
- D = 7b+1 = 7*17+1 = 119+1 = 120
- E = 2b+1 = 2*17+1 = 34+1 = 35 degrees
- F = b+8 = 17+8 = 25
As a check,
D+E+F = 120+35+25 = 120+60 = 180
which helps confirm the correct answers.