Answer: 14
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Step-by-step explanation:
The two angles shown are a linear pair. They are adjacent and supplementary.
Supplementary angles add to 180
(8x+1) + (4x+11) = 180
8x+1+4x+11 = 180
(8x+4x) + (1+11) = 180
12x+12 = 180
12x+12-12 = 180-12 ... subtract 12 from both sides
12x = 168
12x/12 = 168/12 ... divide both sides by 12
x = 14