.
The sum of interior angles of a triangle is 180 degs.
Therefore,
(x-12) + (x-8) + (4x+20) = 180,
6x = 180 ----> x = = 30 ---->
< A = x - 12 = 30 - 12 = 18 degs,
< B = x - 8 = 30 - 8 = 22 degs,
< C = 4x + 20 = 4*30 + 20 = 140 degs.
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