All angles in a triangle sum to 180°, so
(7x - 8) + (3x + 3) + (18x - 11) = 180
28x - 16 = 180
28x = 196
x = 7
(18x - 11) is the clearly largest angle
18(7) - 11 = 115°
115° is an obtuse angle, therefore the triangle is obtuse
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