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Answer:
n = 16
Explanation:
Angle ABC is the sum of its parts.
∠ABC = ∠ABF +∠FBC
159° = (7n +20)° +(2n -5)°
159° = 9n° +15° . . . . . . . . . . . . . . collect terms
144° = 9n° . . . . . . . . . . subtract 15°
16° = n°
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