Hi there!
[tex]\large\boxed{x = 8}[/tex]
Recall that all angles in a triangle sum up to 180°, therefore:
(9x + 3) + (5x - 2) + (11x - 21) = 180
Combine like terms:
9x + 5x + 11x + 3 - 2 - 21 = 180
25x -20 = 180
Add 20 to both sides:
25x = 200
Divide both sides by 25:
x = 8°
