Question 1069834
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The sum of interior angles of any triangle is 180 degrees.

You, probably, know it.


Therefore, for your triangle, 54 + 6x + 6x = 180 degs,  or


54 + 12x = 180,   or   12x = 180 - 54  --->  12x = 126  --->  x = {{{126/12}}} = 10.5 degrees.
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