Answer: choice B, 40.5 degrees
The triangle is isosceles based on the fact that AC = BC (the tick marks are the same). The angles opposite the congruent sides are also congruent
angle A = angle B = x for some unknown number x
The three angles A,B,C add to 180, so,
A+B+C = 180
x+x+99 = 180
2x+99 = 180
2x = 180-99
2x = 81
x = 81/2
x = 40.5
So angle A and angle B are both 40.5 degrees
Check:
A+B+C = 180
40.5+40.5+99 = 180
180 = 180 answer is confirmed
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Edit
The sides with the two tick marks are the same length, so 7x-4 is the same as length as 31
7x-4 = 31
7x = 31+4
7x = 35
x = 35/7
x = 5
Answer is choice B) 5