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Answer:
x = 5
Step-by-step explanation:
39° + 90° + (7x + 16)° = 180°
39 + 90 = 129
180 - 129 = 51
7x + 16 = 51
7x + 16 - 16 = 51 - 16
7x = 35
7x/7 = 35/7
x = 5