Answer: D) 55 degrees
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Work Shown:
A+B+C = 180 ..... angles of a triangle add to 180
(7x+6) + (80) + (3+6x) = 180
13x + 89 = 180
13x = 180-89 .... subtract 89 from both sides
13x = 91
x = 91/13 .... divide both sides by 13
x = 7
Use this x value to find the missing angle measures.
angle A = 7x+6 = 7*7+6 = 55
angle C = 3+6x = 3+6*7 = 45
Note that,
A+B+C = 55+80+45 = 180
which helps confirm our answer.